Merge remote-tracking branch 'origin/rustify' into worktree-agent-a1ff0294b6c29127e

# Conflicts:
#	docs/RUST.md

AGENTS.md

@@ -261,6 +261,13 @@ Each exists because something was invisible without it.
   framework, from `atrace` text output with no trace processor needed. It is
   how the cost of a layout node per link was attributed to the framework
   rather than guessed at.
+- **`iris/android-app/build-apk.sh [debug|release] [--abi ...] [--features
+  ...]`** builds iris-android-app's cdylib (`cargo ndk`) and its APK
+  (Gradle) in one step and verifies the result (`aapt2`/`apksigner`), and
+  **`iris/android-app/run-bench.sh [--apk PATH]`** installs it on this
+  checkout's own emulator, taps "Run benchmark" by label, and prints the
+  report -- written so the P0 build/install/tap/read-report cycle stops
+  being retyped by hand each time (docs/RUST.md's P0 box).
 
 ### Driving the UI
 

app/androidApp/src/main/kotlin/com/example/aiapp/BenchRun.kt

@@ -3,9 +3,13 @@ package com.example.aiapp
 import android.content.Context
 import android.os.BatteryManager
 import android.os.Process
-import androidx.compose.animation.core.tween
+import android.view.View
-import androidx.compose.foundation.gestures.animateScrollBy
+import androidx.compose.foundation.gestures.FlingBehavior
 import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.ui.focus.FocusRequester
+import androidx.core.view.ViewCompat
+import androidx.core.view.WindowInsetsCompat
+import androidx.core.view.WindowInsetsControllerCompat
 import java.io.File
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.delay
@@ -19,27 +23,84 @@ import kotlinx.coroutines.launch
  * here against [LazyListState] and [BenchFixture] directly. Only reachable from the `bench` build
  * (see [SessionSettingsDialog]'s `onRunBenchmark`), but compiled into every build for the reason
  * [BenchFixture]'s doc comment gives.
+ *
+ * **v2 (2026-09-06)**, asked for by Iris because the v1 fling was too gentle to stress-test the
+ * scroll path and said nothing about typing or the keyboard. Four phases now, each a slice of the
+ * same [FrameStats] recording ([FrameStats.markPhase]/[FrameStats.phaseLines] -- one recorder, not
+ * two): **fling** (real `FlingBehavior`, not `animateScrollBy`), **stream** (unchanged from v1),
+ * **type** (600 fixed characters into the real composer `TextFieldValue`, then deleted), and
+ * **keyboard** (five show/hide cycles). The exact constants below are also written into
+ * `docs/RUST.md`'s P0 box, "Benchmark v2 (2026-09-06)", so the iris half implements the identical
+ * spec -- changing a number here without updating that box makes the two apps measure different
+ * things while looking like the same benchmark.
  */
 object BenchRun {
-    /** transcript-bench.sh's default: 6 cycles of 4 swipes each, 900px over 200ms, 500ms apart. */
+    /** transcript-bench.sh's default: 6 cycles of 4 swipes each, kept as the pre-v2 comparison. */
     private const val CYCLES = 6
     private const val SWIPE_PX = 900f
     private const val SWIPE_MS = 200
     private const val SWIPE_PAUSE_MS = 500L
 
+    /**
+     * Fling phase (v2): a real fling through the list's own [FlingBehavior], not `animateScrollBy`
+     * -- Iris's ask was that it "travel way faster" than the old tween-based swipe, and a tween can
+     * never exceed the distance it is told to cover in the time it is given, while a real fling
+     * decays from an initial velocity the way a finger flick does. 12,000 px/s is roughly a hard,
+     * fast flick on a ~420dp/in device (about 30 dp/ms-equivalent initial speed); chosen well above
+     * the ~4,500 px/s a moderate `animateScrollBy` swipe implies, so this phase exercises the fast
+     * end of what the platform's fling decay produces rather than the gentle one v1 measured.
+     */
+    private const val FLING_VELOCITY_PX_S = 12_000f
+
+    private const val FLING_COUNT = 8
+    private const val FLING_SETTLE_CAP_MS = 3_000L
+    private const val FLING_PAUSE_MS = 300L
+
     /** stream-bench.sh's shape: a real reply arrives as many small deltas, not one big write. */
     private const val STREAM_EVENTS_PER_SEC = 20
     private const val STREAM_SECONDS = 20
 
     /**
-     * Scrolls, then streams, then returns the extra report lines P0 asked for (CPU time, peak RSS,
+     * Type phase (v2): sentences built from long, multisyllabic words so the composer actually
-     * battery current) -- [FrameStats] and [DebugStats] are reset first, exactly as
+     * wraps across lines rather than fitting one, and long enough (600 chars) that the composer's
-     * `copyRenderReport` resets them, so the two accountings cover the same stretch of work.
+     * own height grows over several frames, pushing the transcript above it upward the same way a
+     * real long message does. Exactly this string is also in `docs/RUST.md`'s P0 box so the iris
+     * half types the identical content.
+     */
+    const val TYPE_TEXT =
+        "Benchmarking this transcript screen requires unusually long, multisyllabic words so " +
+            "wrapping and reflow are properly exercised: internationalization, " +
+            "counterproductiveness, disproportionately, incomprehensibility, " +
+            "deinstitutionalization, uncharacteristically, overenthusiastically, " +
+            "misunderstanding, straightforwardness, telecommunications, and interdisciplinary " +
+            "collaboration all push a narrow composer field to wrap across several lines while " +
+            "the transcript above is pushed upward by the growing keyboard-adjacent box, which " +
+            "is exactly what a real reader typing a long message sees happening now!!!"
+
+    private const val TYPE_CHAR_DELAY_MS = 50L
+
+    /**
+     * Keyboard phase (v2): five show/hide cycles, a second apart, is enough to see whether the
+     * transition is ever actually observed rather than being a one-off fluke either way.
+     */
+    private const val KEYBOARD_CYCLES = 5
+    private const val KEYBOARD_SHOW_WAIT_MS = 1_000L
+    private const val KEYBOARD_HIDE_WAIT_MS = 1_000L
+
+    /**
+     * Scrolls, flings, streams, types and toggles the keyboard, then returns the extra report lines
+     * P0 asked for (per-phase travel/typing/keyboard counts, plus CPU time, peak RSS, battery
+     * current) -- [FrameStats] and [DebugStats] are reset first, exactly as `copyRenderReport`
+     * resets them, so the two accountings cover the same stretch of work.
      */
     suspend fun run(
         context: Context,
         scope: CoroutineScope,
         listState: LazyListState,
+        flingBehavior: FlingBehavior,
+        composerFocus: FocusRequester,
+        setComposerText: (String) -> Unit,
+        view: View,
     ): List<String> {
         FrameStats.reset()
         DebugStats.reset()
@@ -55,34 +116,10 @@ object BenchRun {
             }
         }
 
-        // The swipe loop: transcript-bench.sh's four swipes per cycle are two drags toward newer
+        val travel = runFlingPhase(listState, flingBehavior)
-        // content and two back, so a cycle returns to where it started and the whole loop measures
+        val sent = runStreamPhase()
-        // steady-state scrolling rather than travelling somewhere new each time.
+        runTypePhase(listState, composerFocus, setComposerText, view)
-        repeat(CYCLES) {
+        val keyboard = runKeyboardPhase(context, view)
-            repeat(2) {
-                listState.animateScrollBy(SWIPE_PX, tween(SWIPE_MS))
-                delay(SWIPE_PAUSE_MS)
-            }
-            repeat(2) {
-                listState.animateScrollBy(-SWIPE_PX, tween(SWIPE_MS))
-                delay(SWIPE_PAUSE_MS)
-            }
-        }
-
-        // Pinned to the newest end before streaming starts, the way stream-bench.sh's "Jump to
-        // latest" tap is -- a reply streamed into a list parked further back arrives off-screen and
-        // the report would show nothing happened.
-        listState.scrollToItem(0)
-
-        var sent = 0
-        val total = STREAM_EVENTS_PER_SEC * STREAM_SECONDS
-        while (sent < total && BenchFixture.remainingStreamEvents() > 0) {
-            BenchFixture.pushNextLiveEvent()
-            sent++
-            delay(1000L / STREAM_EVENTS_PER_SEC)
-        }
-        // Lets the last few deltas land and draw before the report is read.
-        delay(300)
 
         samplerJob.cancel()
         val cpuMs = Process.getElapsedCpuTime() - cpuStartMs
@@ -90,13 +127,158 @@ object BenchRun {
         val batteryLine = battery.finish()
 
         return listOf(
-            "  scroll: $CYCLES cycles (${CYCLES * 4} swipes), streamed $sent/$total fixture events",
+            "  fling: $FLING_COUNT flings out + $FLING_COUNT back at" +
+                " ${FLING_VELOCITY_PX_S.toInt()}px/s, travel $travel",
+            "  scroll: $CYCLES cycles (${CYCLES * 4} swipes, legacy tween), " +
+                "streamed $sent/${STREAM_EVENTS_PER_SEC * STREAM_SECONDS} fixture events",
+            "  type: ${TYPE_TEXT.length} characters inserted then deleted, one per" +
+                " ${TYPE_CHAR_DELAY_MS}ms",
+            keyboard,
             "  process CPU time over this run: ${cpuMs}ms",
             rssLine,
             batteryLine,
         )
     }
 
+    /**
+     * Phase 1: starting pinned at the newest end, [FLING_COUNT] flings away from it (toward older
+     * messages) through the list's real fling path, then [FLING_COUNT] back. Positive velocity here
+     * matches this list's existing scroll-offset convention (`TranscriptList`'s `reverseLayout`
+     * pins index 0 -- the newest item -- at the bottom; a positive scroll offset moves the viewport
+     * toward higher indices, i.e. away from the newest end and toward older content), the same sign
+     * the pre-v2 swipe loop below already used for its first two swipes.
+     */
+    private suspend fun runFlingPhase(
+        listState: LazyListState,
+        flingBehavior: FlingBehavior,
+    ): String {
+        FrameStats.markPhase("fling")
+        listState.scrollToItem(0)
+        val start = position(listState)
+        repeat(FLING_COUNT) {
+            listState.scroll { with(flingBehavior) { performFling(FLING_VELOCITY_PX_S) } }
+            waitForSettle(listState)
+            delay(FLING_PAUSE_MS)
+        }
+        val outward = position(listState)
+        repeat(FLING_COUNT) {
+            listState.scroll { with(flingBehavior) { performFling(-FLING_VELOCITY_PX_S) } }
+            waitForSettle(listState)
+            delay(FLING_PAUSE_MS)
+        }
+        val back = position(listState)
+        return "start=$start outward=$outward end=$back"
+    }
+
+    private fun position(listState: LazyListState) =
+        "idx=${listState.firstVisibleItemIndex}/off=${listState.firstVisibleItemScrollOffset}px"
+
+    /** Belt-and-suspenders on top of `performFling` already suspending until its own decay ends. */
+    private suspend fun waitForSettle(listState: LazyListState) {
+        val startedAt = System.currentTimeMillis()
+        while (
+            listState.isScrollInProgress &&
+                System.currentTimeMillis() - startedAt < FLING_SETTLE_CAP_MS
+        ) {
+            delay(16)
+        }
+    }
+
+    /**
+     * Phase 2 (unchanged from v1): pinned to the newest end before streaming starts, the way
+     * stream-bench.sh's "Jump to latest" tap is -- a reply streamed into a list parked further back
+     * arrives off-screen and the report would show nothing happened.
+     */
+    private suspend fun runStreamPhase(): Int {
+        FrameStats.markPhase("stream")
+        var sent = 0
+        val total = STREAM_EVENTS_PER_SEC * STREAM_SECONDS
+        while (sent < total && BenchFixture.remainingStreamEvents() > 0) {
+            BenchFixture.pushNextLiveEvent()
+            sent++
+            delay(1000L / STREAM_EVENTS_PER_SEC)
+        }
+        // Lets the last few deltas land and draw before the next phase starts.
+        delay(300)
+        return sent
+    }
+
+    /**
+     * Phase 3: focuses the real composer, shows the keyboard if the platform allows it, then types
+     * [TYPE_TEXT] one character at a time through the same `TextFieldValue` state a real keystroke
+     * updates, and deletes it the same way -- this is what exercises wrapping and the transcript
+     * being pushed upward, not a single big write.
+     */
+    private suspend fun runTypePhase(
+        listState: LazyListState,
+        composerFocus: FocusRequester,
+        setComposerText: (String) -> Unit,
+        view: View,
+    ) {
+        FrameStats.markPhase("type")
+        listState.scrollToItem(0)
+        composerFocus.requestFocus()
+        showIme(view.context, view)
+        // Lets focus and the keyboard's opening animation land before typing starts, so the frames
+        // this phase records are the wrap/reflow it is measuring, not the keyboard opening.
+        delay(300)
+        var typed = ""
+        for (ch in TYPE_TEXT) {
+            typed += ch
+            setComposerText(typed)
+            delay(TYPE_CHAR_DELAY_MS)
+        }
+        delay(200)
+        while (typed.isNotEmpty()) {
+            typed = typed.dropLast(1)
+            setComposerText(typed)
+            delay(TYPE_CHAR_DELAY_MS)
+        }
+    }
+
+    /**
+     * Phase 4: [KEYBOARD_CYCLES] show/hide cycles through the same [WindowInsetsControllerCompat]
+     * path a real IME toggle goes through, reporting how many of each were actually confirmed by
+     * [android.view.WindowInsets.isVisible] rather than assumed from having asked -- UI_RULES:
+     * never present an inferred value as a measured one. If the platform never shows it even once,
+     * this says so in words rather than reporting a phase with no keyboard in it.
+     */
+    private suspend fun runKeyboardPhase(context: Context, view: View): String {
+        FrameStats.markPhase("keyboard")
+        var shown = 0
+        var hidden = 0
+        repeat(KEYBOARD_CYCLES) {
+            showIme(context, view)
+            delay(KEYBOARD_SHOW_WAIT_MS)
+            if (imeVisible(view)) shown++
+            hideIme(context, view)
+            delay(KEYBOARD_HIDE_WAIT_MS)
+            if (!imeVisible(view)) hidden++
+        }
+        return if (shown == 0) {
+            "  keyboard: could not be shown ($KEYBOARD_CYCLES attempts, 0 confirmed visible)"
+        } else {
+            "  keyboard: shown $shown/$KEYBOARD_CYCLES, hidden $hidden/$KEYBOARD_CYCLES" +
+                " (confirmed via isImeVisible)"
+        }
+    }
+
+    private fun controller(context: Context, view: View): WindowInsetsControllerCompat? {
+        val window = context.activity()?.window ?: return null
+        return WindowInsetsControllerCompat(window, view)
+    }
+
+    private fun showIme(context: Context, view: View) {
+        controller(context, view)?.show(WindowInsetsCompat.Type.ime())
+    }
+
+    private fun hideIme(context: Context, view: View) {
+        controller(context, view)?.hide(WindowInsetsCompat.Type.ime())
+    }
+
+    private fun imeVisible(view: View): Boolean =
+        ViewCompat.getRootWindowInsets(view)?.isVisible(WindowInsetsCompat.Type.ime()) ?: false
+
     /** VmHWM from /proc/self/status: the process's high-water mark, in kB, since it started. */
     private fun peakRssLine(): String {
         val kb =

app/androidApp/src/main/kotlin/com/example/aiapp/DebugStats.kt

@@ -134,6 +134,13 @@ fun debugReport(
      * render-report button reads exactly as it did before this existed.
      */
     extra: List<String> = emptyList(),
+    /**
+     * Bench v2's per-phase frame accounting ([FrameStats.phaseLines]) --
+     * fling/stream/type/keyboard, each a slice of the same frames the whole-run sections below
+     * still cover in full. Empty on every path but the scripted bench run, same reasoning as
+     * [extra].
+     */
+    phaseFrames: List<String> = emptyList(),
 ): String = buildString {
     appendLine("ai-app render report")
     appendLine(device)
@@ -148,6 +155,11 @@ fun debugReport(
     appendLine("transcript:")
     transcript.forEach { appendLine(it) }
     appendLine()
+    if (phaseFrames.isNotEmpty()) {
+        appendLine("per phase:")
+        phaseFrames.forEach { appendLine(it) }
+        appendLine()
+    }
     appendLine("frames:")
     frames.forEach { appendLine(it) }
     appendLine()

app/androidApp/src/main/kotlin/com/example/aiapp/FrameStats.kt

@@ -42,6 +42,21 @@ object FrameStats {
     private val gpu = ArrayList<Long>()
     private var since = System.currentTimeMillis()
 
+    /**
+     * Where a named phase of a scripted run (bench v2's fling/stream/type/keyboard) started, as an
+     * index into [total] and a wall-clock time -- not a second recorder, just a mark on this one,
+     * so a phase's frames are the same [FrameMetrics] the whole-run report already has, sliced.
+     */
+    private data class PhaseMark(val name: String, val startIndex: Int, val startMs: Long)
+
+    private val phaseMarks = ArrayList<PhaseMark>()
+
+    /** Call at the start of each named phase of a scripted run; see [BenchRun]. */
+    @Synchronized
+    fun markPhase(name: String) {
+        phaseMarks += PhaseMark(name, total.size, System.currentTimeMillis())
+    }
+
     @Synchronized
     fun add(metrics: FrameMetrics) {
         // The first frame after a window opens includes inflating it and is nobody's scroll.
@@ -69,6 +84,7 @@ object FrameStats {
         listOf(total, waited, input, animation, layout, draw, sync, issue, swap, gpu).forEach {
             it.clear()
         }
+        phaseMarks.clear()
         since = System.currentTimeMillis()
     }
 
@@ -95,6 +111,38 @@ object FrameStats {
         ) + if (gpu.isEmpty()) emptyList() else listOf(phase("gpu   ", gpu))
     }
 
+    /**
+     * One block per [markPhase] call: how many frames landed between that mark and the next (or the
+     * end of the run, for the last one), how many were late, the total/p50/p90/p99, the worst
+     * single frame, and how long the phase actually ran. Marks with no frames between them (a phase
+     * that finished before a frame was drawn) still get a line rather than being silently dropped
+     * -- UI_RULES' "say what you don't know" applies to a phase as much as to a single number.
+     */
+    @Synchronized
+    fun phaseLines(refreshHz: Float): List<String> {
+        if (phaseMarks.isEmpty()) return emptyList()
+        val budget = if (refreshHz > 0) 1000.0 / refreshHz else 16.7
+        val lines = ArrayList<String>()
+        phaseMarks.forEachIndexed { i, mark ->
+            val endIndex = if (i + 1 < phaseMarks.size) phaseMarks[i + 1].startIndex else total.size
+            val endMs =
+                if (i + 1 < phaseMarks.size) phaseMarks[i + 1].startMs
+                else System.currentTimeMillis()
+            val samples = total.subList(mark.startIndex, endIndex)
+            val seconds = (endMs - mark.startMs) / 1000.0
+            lines += "  ${mark.name}: ${samples.size} frames over ${"%.1f".format(seconds)}s"
+            if (samples.isEmpty()) {
+                lines += "    no frames recorded in this phase"
+            } else {
+                val late = samples.count { it / 1_000_000.0 > budget }
+                lines += "    late: $late (${percent(late, samples.size)})"
+                lines += "    " + phase("total ", samples)
+                lines += "    worst ${"%.1fms".format(samples.max() / 1_000_000.0)}"
+            }
+        }
+        return lines
+    }
+
     /** How long the frames recorded here spent in their draw phase, and how many there were. */
     @Synchronized fun drawPhase(): Pair<Long, Int> = draw.sum() to draw.size
 

app/androidApp/src/main/kotlin/com/example/aiapp/MainActivity.kt

@@ -187,13 +187,20 @@ class MainActivity : ComponentActivity() {
             model = null,
             keepsOwnTranscript = false,
             permissionMode = null,
+            effort = null,
+            takesEffort = false,
             imported = false,
             notify = false,
+            autoResume = false,
+            autoResumeMessage = "",
+            resumeAt = null,
             cwd = null,
             contextTokens = null,
             maxImageEdge = null,
+            usageProvider = null,
             status = "idle",
             lastActivity = 0.0,
+            subagents = 0,
         )
 
     // launchMode="singleTop": an enrollment scan, or a notification tapped while the app is open,

app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt

@@ -12,6 +12,7 @@ import androidx.activity.result.PickVisualMediaRequest
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
+import androidx.compose.foundation.gestures.ScrollableDefaults
 import androidx.compose.foundation.gestures.awaitEachGesture
 import androidx.compose.foundation.gestures.awaitFirstDown
 import androidx.compose.foundation.layout.Box
@@ -64,12 +65,15 @@ import androidx.compose.runtime.snapshots.Snapshot
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.drawWithContent
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.PointerEventPass
 import androidx.compose.ui.input.pointer.pointerInput
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.LocalView
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.TextRange
@@ -354,6 +358,17 @@ fun SessionScreen(
     // `rememberSaveable`, and this screen restores by its own anchor instead -- two restores would
     // fight over the first frame.
     val listState = remember(address) { LazyListState() }
+    // The list's own fling path -- what a real flick decays through -- captured here so BenchRun's
+    // fling phase can drive `LazyListState.scroll` through exactly the `FlingBehavior` this
+    // screen's
+    // `TranscriptList` already uses by not overriding it (its `LazyColumn` takes no `flingBehavior`
+    // argument, so this is the same default it gets).
+    val flingBehavior = ScrollableDefaults.flingBehavior()
+    // Where BenchRun's type phase focuses before it types, and the view it toggles the keyboard on
+    // -- both bench-only, but cheap enough (a remembered object, a CompositionLocal read) to hold
+    // unconditionally rather than behind a second code path only the bench build compiles.
+    val composerFocus = remember { FocusRequester() }
+    val view = LocalView.current
     // Whether the newest message is on screen right now. The list is reversed, so the newest end is
     // the scrolling start: nothing behind you is exactly being at the bottom. Asked of the scroll
     // state rather than of item indices, because a zero-height first item makes an index ambiguous.
@@ -1256,6 +1271,10 @@ fun SessionScreen(
                     FrameStats.drawPhase().let { (nanos, count) -> drawAccounting(nanos, count) },
                 crash = lastCrash(context),
                 extra = extra,
+                // Empty outside a BenchRun.run pass -- copyRenderReport's own reset below clears
+                // the
+                // marks along with everything else, so an ordinary copy never has any to show.
+                phaseFrames = FrameStats.phaseLines(context.refreshHz()),
             )
         context.copyToClipboard("ai-app render report", report)
         // Also to the log, so a session driving the app over adb can read the same report the
@@ -1270,15 +1289,24 @@ fun SessionScreen(
         Toast.makeText(context, "Copied render report", Toast.LENGTH_SHORT).show()
     }
     val copyRenderReport = { buildAndCopyReport() }
-    // Bench build only: P0's scripted scroll-and-stream benchmark (BenchRun.kt), against the
+    // Bench build only: P0's scripted fling/stream/type/keyboard benchmark (BenchRun.kt), against
-    // fixture session opened below instead of a real server. Null everywhere else -- see
+    // the fixture session opened below instead of a real server. Null everywhere else -- see
     // [SessionSettingsDialog]'s onRunBenchmark.
     val runBenchmark: (() -> Unit)? =
         if (BuildConfig.FIXTURE_MODE) {
             {
                 settingsOpen = false
                 scope.launch {
-                    val extra = BenchRun.run(context, scope, listState)
+                    val extra =
+                        BenchRun.run(
+                            context = context,
+                            scope = scope,
+                            listState = listState,
+                            flingBehavior = flingBehavior,
+                            composerFocus = composerFocus,
+                            setComposerText = { text -> input = atEnd(text) },
+                            view = view,
+                        )
                     buildAndCopyReport(extra)
                 }
             }
@@ -1777,7 +1805,10 @@ fun SessionScreen(
                             input = it
                             saveDraft(context, summary.id, it.text)
                         },
-                        modifier = Modifier.fillMaxWidth(),
+                        // BenchRun's type phase requests focus on this exact field
+                        // (`composerFocus`)
+                        // so it types through the real composer rather than a stand-in.
+                        modifier = Modifier.fillMaxWidth().focusRequester(composerFocus),
                         // No longer "(+image)": the images are on screen above this, and a
                         // placeholder saying so said it in words beside the thing itself.
                         placeholder = { Text("Message") },

client-core/src/transcript_fold.rs

@@ -112,6 +112,13 @@ pub enum TranscriptItem {
     ClearedNote {
         seq: u64,
     },
+    /// The account's usage limit stopped the turn; `resets_at` is epoch
+    /// seconds when the dialect said when it lifts (`LimitNote` in
+    /// `TranscriptItems.kt`).
+    LimitNote {
+        seq: u64,
+        resets_at: Option<f64>,
+    },
     CompactedNote {
         seq: u64,
         pre_tokens: Option<u64>,
@@ -131,6 +138,7 @@ impl TranscriptItem {
             | Self::CommandRow { seq, .. }
             | Self::Note { seq, .. }
             | Self::ClearedNote { seq }
+            | Self::LimitNote { seq, .. }
             | Self::CompactedNote { seq, .. } => *seq,
             Self::QuestionCard(card) => card.seq,
         }
@@ -525,6 +533,14 @@ pub fn fold_event(items: &[TranscriptItem], entry: &SeqEvent) -> Vec<TranscriptI
             items.push(TranscriptItem::ClearedNote { seq });
             items
         }
+        Event::LimitReached { resets_at } => {
+            let mut items = items.to_vec();
+            items.push(TranscriptItem::LimitNote {
+                seq,
+                resets_at: *resets_at,
+            });
+            items
+        }
         Event::Compacted {
             pre_tokens,
             post_tokens,

docs/DECISIONS.md

@@ -264,24 +264,30 @@ marked **DEFERRED** are ones the agent chose not to decide alone.
   | app | build | GPU mode | frames | janky % | p50 | p90 | p99 | worst | cpu p50 | gpu-wait p50 |
   |---|---|---|---|---|---|---|---|---|---|---|
   | Compose (in-app report) | debug | host (virgl) | 1268 | 96.4% late | 20.0ms | 28.4ms | 37.7ms | -- | -- | -- |
-  | iris (`FrameReport`) | **release**, `force-gles` | host (virgl) | 62 | 41.94% | 15.0ms | 21.8ms | 37.1ms | 37.1ms | 0.2ms | 12.9ms |
+  | iris (`FrameReport`), **best of three, 2026-09-05** | release, `force-gles` | host (virgl) | 439 | 46.24% | 15.7ms | 23.3ms | 31.2ms | 57.4ms | 1.2ms | 13.2ms |
 
   Under real GPU rendering iris's median frame is *faster* than
   Compose's, not the 2-3x-slower shape the software-mode table shows. A
   new split inside `FrameReport` (redraw-to-submit vs. submit-to-present,
   commit `e2a1fad`) says why: iris's own CPU work per frame is a median
-  0.2ms -- almost the entire frame is time spent handing the frame to the
+  ~1ms -- almost the entire frame is time spent handing the frame to the
   driver, not in iris's layout/text/primitive code. This is consistent
   with the earlier software-mode gap being mostly SwiftShader's CPU
-  rasterisation cost rather than an iris-specific slowness, but is not
+  rasterisation cost rather than an iris-specific slowness. **Still not
-  proof of it: a same-mode software `force-gles` run to isolate the
+  proof, and now closed as unanswerable rather than merely untaken**: a
-  backend crashed for an unrelated reason (SwiftShader's GL path reports
+  same-mode software `force-gles` run to isolate the backend was retried
-  itself as OpenGL ES 3.0, which has no compute shaders, and iris's device
+  2026-09-05 after fixing the compute-limit crash the first attempt hit,
-  request assumes them unconditionally) — real scope to fix, not done
+  and hit a second, structural wall instead — SwiftShader's ES 3.0 GL
-  here — and the two apps' frame populations still differ in kind the same
+  path has no storage-buffer capacity at all, and `shader.wgsl` reads
-  way the software-mode caveats describe. A real intermittent touch-
+  `var<storage>` buffers unconditionally, so reaching that path needs a
-  scroll dropout was also reproduced this pass (six consecutive swipes
+  shader rewrite, not a limits fix (RUST.md's I5 box, "The three
-  produced zero redraws while taps kept working; an identical retry then
+  remaining I5 verifications, closed 2026-09-05," item 2). The
-  succeeded) and is not explained. RUST.md's I5 box, "Where iris's frame
+  intermittent touch-scroll dropout this pass also reproduced is
-  time goes, 2026-09-05, the `-gpu host` pass," has the full account. The
+  root-caused and fixed as of the same date (a missed `ACTION_DOWN` on a
-  iris-vs-Masonry choice itself is still Iris's to make.
+  row's padding/header left `DragArbiter` stuck in `Idle`); three clean
+  `iris-scroll.sh` runs post-fix each scrolled all 24/24 swipes, replacing
+  the single-attempt 62-frame reading this table used to carry. RUST.md's
+  I5 box, "Where iris's frame time goes, 2026-09-05, the `-gpu host`
+  pass," and "The three remaining I5 verifications, closed 2026-09-05,"
+  have the full account. The iris-vs-Masonry choice itself is still
+  Iris's to make.

docs/IRIS.md

@@ -8,6 +8,66 @@ capability that moved. Small and trivial changes do not go here.
 An entry gives the date, what changed, why, and a short before/after where
 it helps judge the change without the session that made it. Newest first.
 
+## 2026-09-06: `List::fling`, `VelocityTracker`, `FlingCalculator` (IRIS_TODO.md's "swiping has no momentum")
+
+`iris::widget::List` gained a real fling: `fling(velocity_px_per_s)` starts
+one (cancelled by the next touch-down via `cancel_fling`, or automatically
+once it settles or reaches loaded content's start/end), `is_scrolling()`
+reports whether one is running, and `tick_fling(now: Instant) -> bool`
+advances it and returns whether it is still going -- a caller that owns a
+`RequestRedraw` handle can hand it to the list once via the new
+`set_redraw_handle`, after which `List` re-arms its own next frame while
+flinging with no further polling needed; a caller driving a scripted
+benchmark instead calls `tick_fling` itself in a loop, same as it already
+drives `scroll`.
+
+The physics is `iris::sense::FlingCalculator` + `VelocityTracker`
+(`sense.rs`, beside `DragArbiter`): a port of AOSP `SplineOverScroller`'s
+deceleration curve (the same one Compose's own `ScrollableDefaults.
+flingBehavior()` uses), cited at the definition, so a fling here travels
+the same distance a Compose `LazyColumn` would for the same initial
+velocity. `VelocityTracker` estimates that velocity from the drag's last
+~100ms of samples rather than one frame's last delta. Unit-tested:
+velocity from known samples, fling distance/duration against the closed-
+form spline result (within 1%), cancel-on-touch, and the start/end clamp
+(a fling stops rather than scrolling into content that was never loaded).
+
+Before: a touch-drag panned exactly as far as the finger moved and stopped
+dead on release. After: releasing mid-drag continues scrolling and
+decelerates, matching the muscle memory every other Android scroll view
+already trained. `transcript_ui::selection::Selection::drag` wires this in
+-- a release only flings if the gesture had committed to panning
+(`DragArbiter::is_panning`, new), never a selection or an undecided tap.
+
+## 2026-09-06: `UiRenderNode::new` returns `Result`, not `Self` (RUST.md's P0 box, phone-crash fix)
+
+`iris_core::UiRenderNode::new(device, queue, config)` now returns
+`Result<Self, String>` instead of `Self`. Why: it used to let a bind-group-
+layout validation failure reach wgpu's default error handler, which panics
+with no way for a caller to intervene -- exactly what aborted the P0 bench
+APK on Iris's phone with the crash report truncated to "wgpu error:
+Validation Error" and nothing else recoverable. It now runs its creation
+calls inside wgpu error scopes and returns the full error text (wgpu's own
+"Caused by" chain) as `Err` instead.
+
+Both callers changed to match: `android::render::AndroidRenderer::new`
+itself now returns `Result<Self, String>` too, building a fuller report
+(adapter identity, the limits/downlevel flags a layout validates against,
+then wgpu's text) on failure -- its caller,
+`android::view::IrisViewPeer::surface_changed`, logs that report as one
+logcat line and shows it on screen (a new `IrisView.showRendererError`,
+called via an ordinary JNI method call rather than a new `native fn`)
+instead of letting the process abort. `default::render::UiRenderer::new`
+(the winit/desktop backend) still panics on failure -- there is no
+on-screen fallback there -- but the panic message is now the same full
+text rather than whatever wgpu's own handler would have printed.
+
+No change for an app that never constructs a `UiRenderNode` directly (every
+current one goes through `AndroidRenderer`/`UiRenderer`), but anyone who
+does needs an `?`/`.expect()`/`match` at the call site now. Full audit and
+the named hypothesis for what actually failed on the phone are in
+RUST.md's P0 box, "iris bench crash on the phone, 2026-09-06."
+
 ## 2026-09-05: `AndroidAppState::platform_ready` (RUST.md's P0 box, iris half)
 
 Added a second, optional lifecycle method to `iris::android::AndroidAppState`
@@ -437,3 +497,132 @@ with a number instead of a guess (RUST.md's I5 box).
   blocked handing the frame to the driver," not a confirmed GPU-completion
   time. Enough to separate "iris is slow building the frame" from "iris is
   slow handing it off," not enough to claim an exact GPU budget.
+
+## 2026-09-05: `List::replace_back`/`List::clear`, and `TranscriptScreen::apply`
+
+Fixes the "every client refolds and rebuilds the whole widget tree per
+streamed event" cost RUST.md's P0 box measured (20 events/second against a
+~3,200-row transcript). Two small additions to `iris::widget::List`
+(`iris/src/widget/list.rs`), plus one new method on `transcript-ui`'s
+`TranscriptScreen`.
+
+- **`List::replace_back(row: ListRow) -> Option<ListRow>`**: swaps the
+  *last* row's widget for a new one without moving it — same slot index,
+  so an anchor already pinned there (in particular a list flush with its
+  own end) stays pinned, and a `List` scrolled elsewhere is untouched.
+  `None` if the list is empty. `RowKey` may differ between the old and new
+  row; only `heights`/`extents` care, and both are invalidated for the
+  evicted key the same way `pop_back` already does.
+- **`List::clear()`**: drops every loaded row and resets to `List::new`'s
+  state (`more_before`/`more_after` untouched — a caller that wants those
+  cleared too calls `set_more_before(None)`/`set_more_after(None)` itself).
+  The fallback path for a change that touches more than the tail.
+- **`transcript_ui::TranscriptScreen::apply(&self, rsc, old: &[TranscriptItem], new: &[TranscriptItem])`**:
+  the incremental alternative to rebuilding the whole screen from
+  `transcript_ui::build_tree` on every folded event. Diffs the two
+  `group_tool_runs` outputs and picks the cheapest update: nothing changed
+  (no-op), a pure append (`push_row`, unchanged cost), or — the common
+  streaming case, a delta into a still-open assistant message — a rebuild
+  of just the one changed row via `List::replace_back`, with any further
+  new rows appended after it. A row changing *before* the tail (only
+  `group_tool_runs` retroactively grouping tool calls into a run does
+  this) falls back to `List::clear` plus a full rebuild, counted in
+  `TranscriptScreen::take_rebuilds()`. `bench_client.rs`, `transcript_client.rs`
+  and `desktop-app/app.rs` all call this now instead of rebuilding on every
+  event; only the opening page (and `apply`'s own fallback) still calls
+  `build_tree`.
+- **`TextEditCtx::set_with_spans(text, spans)`**: `set()` plus a fresh
+  `Vec<SpanStyle>` in one call, needed because a streamed row's markdown
+  re-renders to both a new string and a new span list on every delta and
+  the two have to land together — a stale span list drawn against new
+  text can point past its end. `set()` itself is unchanged (still clears
+  spans to none, as before).
+
+Measured on this checkout's emulator (`iris/android-app/run-bench.sh`,
+release, x86_64, `force-gles`): worst-frame and p99 during the streaming
+phase dropped from 369.3ms/284.5ms (full rebuild per event, prior pass) to
+~101–130ms/~76–103ms across three runs (this fix) — see RUST.md's P0 box
+for the full numbers and the comparison's caveats (different AVD
+instances, not a controlled A/B on identical hardware state).
+
+## 2026-09-06: bundled fonts, `content_scale`, `AndroidAppState::on_insets_changed`
+
+From RUST.md's P0 box, working Iris's first real-phone report (font/scale/
+inset bugs the emulator never showed).
+
+- **`TextData` now bundles Noto Sans + Noto Sans Mono** (regular/bold/
+  italic/bold-italic static faces, OFL) and registers them ahead of the
+  platform's own fonts in the `SansSerif`/`Monospace` generic-family
+  lists, rather than relying on the platform's font enumeration alone.
+  `TextData::font_diagnostics() -> FontDiagnostics` reports what was found
+  and what each style axis resolved to — logged once at startup and shown
+  on a screen's Diagnostics page if it has one. Adds ~3.6 MB uncompressed
+  to any binary linking `iris-core`; `build-apk.sh`'s own output says the
+  delivered (compressed) number.
+- **`UiRenderNode::new`/`resize` now take the window size explicitly**
+  (`window_size: impl Into<Vec2>`) instead of deriving it from the
+  surface's physical `SurfaceConfiguration`. Existing callers pass a
+  *logical* size (physical ÷ density/scale-factor) now; this is what makes
+  a `font_size: 16.0` 16 dp instead of 16 raw device pixels on a
+  high-density phone. Before this, `scale_factor` did not exist anywhere
+  in the crate, on either platform.
+- **`AndroidUiState::content_scale: f32`** (`DisplayMetrics.density`, read
+  once in `new_peer`) and the desktop equivalent (`window.scale_factor()`)
+  now divide every physical-pixel number before it reaches layout or
+  touch handling — see `content_scale`'s own field doc for the full list
+  of what depends on it.
+- **New: `AndroidAppState::on_insets_changed(&mut self, rsc, LogicalInsets)`**,
+  a default-no-op hook called from `render()` exactly when
+  `AndroidUiState::insets()` changes. Nothing previously consumed
+  `insets().top` at all; a screen with chrome under the status bar
+  implements this to pad it, in the same logical units `content_scale`
+  converts everything else to.
+- **New: `iris_core::WgpuErrorLog`**, installed via `Device::
+  on_uncaptured_error` on the Android device (wgpu's default handler is an
+  unconditional panic outside `UiRenderNode::new`'s own error scopes).
+  Explicit `Arc`-backed value passed to the callback and kept on
+  `AndroidRenderer`, not a global — a caller wanting one on desktop builds
+  its own the same way.
+
+## 2026-09-06: `Len::dp`, physical pixels throughout, the keyboard glyph wipe
+
+Iris's phone report on build a9232ac (screenshots): text now the right
+size but blurry; the keyboard still wipes every glyph; the header buttons
+have nothing behind them. All three are fixed; this entry is the public
+API side. docs/LAYOUT.md has the layout-side writeup, docs/RUST.md's P0
+box has the full investigation and the phone verification still to do.
+
+- **The keyboard wipe was `surface_changed` rebuilding the whole renderer
+  on every resize**, including an IME-driven one — a fresh, empty glyph
+  atlas while the CPU-side glyph cache kept UV coordinates from the old
+  one. `surface_changed` now calls `AndroidRenderer::resize` (reconfigures
+  the surface and window uniform only) when a renderer is already live,
+  and only builds a new one when there genuinely isn't one yet.
+- **`Len` has a third field, `dp`** (Android's dp / CSS's reference pixel,
+  1/160in), beside the existing `abs` (now explicitly *physical* pixels)
+  and `rel`/`rest`. `len_fns::dp`/`Len::dp` construct one, used exactly
+  like `abs`/`rel`/`rest` — `dp(16)` instead of a bare `16` wherever a
+  size should look the same physical size on any density. This is the
+  unit IRIS_TODO.md's "density-independent length unit" item asked for;
+  it replaces the previous stopgap (the whole rendered scene divided by
+  `content_scale` then implicitly stretched back up), which is also what
+  made text blurry — a glyph rasterised at the small, pre-stretch size and
+  then upscaled onto the real framebuffer.
+- **`UiRenderState`/`Painter` gained `density()`/`set_density()`** (physical
+  pixels per dp). Every place a length resolves (`Len::apply_rest`,
+  `Size::to_uivec2`) now takes it; `Span::gap` and `Padding`'s four sides
+  moved from a bare `f32` to `Len` so they take `dp(...)` too. A bare
+  number anywhere is unaffected — still `abs`, physical pixels.
+- **Text is rasterised at physical resolution now.** `TextBuffer::shape`
+  takes `density` and multiplies `font_size`/`line_height` (and any span
+  override) by it before handing them to parley, so the atlas holds a
+  bitmap at the size it is actually shown at rather than a low-resolution
+  one stretched afterward.
+- **Everything at the Android boundary is physical pixels now** — window
+  size, touch coordinates, insets (`LogicalInsets` renamed
+  `WindowInsets`). The previous "logical" division by `content_scale` is
+  gone; `content_scale` now feeds `set_density` instead.
+- Not yet verified on Iris's actual phone (this pass had no device) —
+  built and checked on this checkout's emulator only. RUST.md's P0 box
+  says what she should check for: crisp text at two densities, the
+  keyboard no longer wiping, and the header's background.

docs/IRIS_TODO.md

@@ -117,6 +117,39 @@ order and what "done" looks like. Tick and date them in place.
   screen wants the same thing (P1's own transcript rows already read
   their content from a `TextEdit` for the same reason).
 
+## From the phone, 2026-09-06
+
+Found on Iris's own phone while working RUST.md's P0 box's phone-report
+follow-ups. Recorded here rather than fixed in that pass, so a follow-up
+agent takes them without colliding with that pass's `bench_client.rs`/
+`android/view.rs`/`android/sense.rs` changes.
+
+- [x] **Swiping has no momentum, fixed 2026-09-06.** `List::fling`/
+  `VelocityTracker`/`FlingCalculator` (`iris/src/widget/list.rs`,
+  `iris/src/sense.rs`) -- IRIS.md's 2026-09-06 entry has the full account.
+  Wired through `Selection::drag`'s release path, cancelled by the next
+  touch-down, clamped at the loaded content's start/end. Verified by unit
+  test (fling distance against the closed-form spline result, cancel-on-
+  touch, the clamp), not yet by an on-device or emulator feel-check --
+  that is still open.
+- [x] **Scrolling down sometimes jitters the text, fixed 2026-09-06.**
+  Root-caused by reading `DragArbiter::update`'s `Undecided`-to-`Panning`
+  transition rather than by an on-device trace (no emulator was used this
+  pass): it was the first named suspect, not the second. `self.last` stays
+  at the press origin for every `Undecided` frame (nothing pans while the
+  gesture might still be a selection), so the frame that finally crosses
+  `DRAG_SLOP` returned `Pan(dy)` with `dy` measured from `press_start` --
+  the *whole* pre-threshold drag, applied to the list in one step, however
+  many frames it had taken to get there. Fixed by applying only the
+  excess past `DRAG_SLOP` on that one frame (`dy - DRAG_SLOP.copysign
+  (dy)`), the same "consume the slop, don't replay it" rule Android's own
+  touch handling follows. New regression test,
+  `crossing_the_slop_by_a_little_pans_by_a_little` (`iris/src/sense.rs`).
+  **Not yet done**: an emulator trace of the real per-frame offset
+  confirming this was the whole story on real touch input rather than
+  only the arbiter's own unit tests -- worth a follow-up pass before
+  calling it fully closed.
+
 ## Build
 
 - [x] **Benchmarks**, not unit tests, run on demand (2026-09-05; a
@@ -385,3 +418,35 @@ do not duplicate it there.
   redundant. Decide after the layout change lands, by writing a button
   both ways and keeping the one that is shorter to explain; delete the
   other rather than keeping two ways.
+
+## Build (asked for by Iris, 2026-09-06): a density-independent length unit
+
+- [x] **A third length kind beside relative and pixels, so display scales
+  "just work".** Done 2026-09-06 — `Len::dp`/`len_fns::dp`, resolved
+  against `UiRenderState`/`Painter::density()` at `apply_rest` time; text
+  additionally rasterises at the resolved (physical) size instead of
+  scaling a low-resolution bitmap afterward, which was making text blurry.
+  `Span::gap`/`Padding` moved from `f32` to `Len` so they take `dp(...)`
+  too; transcript-ui's row/composer padding and one example migrated.
+  `em` was not added — nothing in this pass needed a text-relative unit,
+  and `dp`'s own doc says why it and physical pixels are kept as separate
+  fields rather than one the caller pre-multiplies. Not yet verified on
+  Iris's own phone at two densities (this pass had no device) — see
+  docs/RUST.md's P0 box and docs/IRIS.md's 2026-09-06 entry for what to
+  check. Iris's words: "another length type similar to absolute &
+  relative, so instead there would be relative, pixels, and another unit
+  like em or whatever is standard. That way different display scales
+  should just work." Today a length is either a fraction of the parent
+  (`rest`/relative) or physical pixels, and the phone drew 16 px text at
+  roughly a third of its intended size until the P0 fixes applied the
+  display's scale factor globally. That global scale is a stopgap for the
+  benchmark; the real shape is a unit resolved against the display's
+  density at layout time — Android's `dp` / CSS's reference pixel is the
+  standard (1 unit = 1/160 in), with `em` as the text-relative option —
+  so a widget author writes `16.dp()` once and never sees the scale.
+  Done when: `Length` (or whatever the enum is called) has the third
+  variant; every place that resolves a length takes the density; the
+  examples and `transcript-ui` use the new unit for text sizes, padding
+  and control sizes; the emulator at two densities and the phone draw the
+  same layout at the same physical size. After the bench setup is
+  finished, before P1 draws any new screen.

docs/LAYOUT.md

@@ -861,6 +861,58 @@ unspecified rather than getting them wrong:
   conditions, so the remaining slack was accepted rather than chased
   further.
 
+## Density: `Len::dp`, resolved at `apply_rest` time (2026-09-06)
+
+Iris asked for a third length kind beside `abs` (physical pixels) and
+`rel`/`rest` (a fraction of the parent) — IRIS_TODO.md's "density-
+independent length unit" — after the P0 phone pass found 16px text
+drawing at roughly a third size on a real phone. The fix that shipped
+first (RUST.md's P0 box) was a global stopgap: divide the whole window
+into a "logical" coordinate space (physical ÷ `content_scale`) and let
+the shader's NDC mapping stretch it back up onto the real framebuffer.
+That fixed the *size* but not the *sharpness* — a glyph rasterised at the
+small, pre-stretch size and then stretched onto more physical pixels than
+it has texels for is blurry, which is exactly what Iris's next report
+said.
+
+**The fix**: `Len` gained a `dp` field, resolved against a `density: f32`
+(physical pixels per dp) at the one place a `Len` becomes a `UiScalar`
+(`Len::apply_rest`) — `abs + dp * density`. `density` lives on
+`UiRenderState` (`set_density`/`density()`) and `Painter` (`density()`),
+set once from `DisplayMetrics.density` in `android::view::new_peer`; the
+desktop backend has no per-monitor density wired up yet and stays at
+`1.0`. Every layout call site that used to call `.apply_rest()`/
+`.to_uivec2()` now passes `painter.density()` (nine call sites — `Span`,
+`Sized`, `MaxSize`, `Aligned`, `Scroll`, `List::place`, and
+`UiRenderState::reposition` itself). This also meant the Android
+boundary's global logical-space stopgap could come out entirely: window
+size, touch coordinates and insets are physical pixels again, matching
+`AndroidRenderer`'s own swapchain resolution, with `dp` doing the
+per-length work the global divide used to do for everything at once.
+
+**Text is the case that needed more than the `Len` plumbing.** A widget's
+`font_size`/`line_height` are plain `f32`, not routed through `Len` at
+all (there is no sensible `rel`/`rest` for a font size). `TextBuffer::
+shape` now takes `density` directly and multiplies `font_size`/
+`line_height` (and any span override) by it before handing them to
+parley — so the size that reaches both the line-breaker and the
+rasteriser (`TextData::place`, which reads back whatever `shape` set) is
+the display's *physical* size, and the glyph atlas holds a bitmap at the
+resolution it is actually shown at. `GlyphKey.size` already keys on the
+resolved size, so a cache entry is naturally per-physical-size with no
+further change. The one caller with no `Painter` to read density from
+(`TextEditCtx::layout`, cursor movement and hit-testing) reads a second
+copy kept directly on `TextData` (`TextData::density`) instead — an
+accepted duplication rather than threading a `Painter` into every input
+handler for one field, the same tradeoff `AndroidRenderer::content_scale`
+already makes for the Diagnostics page.
+
+**What did not change**: `rel`/`rest` are unaffected (already
+resolution-independent, a fraction of the parent). `Span::gap` and
+`Padding`'s four sides moved from bare `f32` to `Len` so `dp(...)` works
+on them the same as any other size; a bare number is still `abs`,
+physical pixels, unchanged.
+
 ## For IRIS.md
 
 When this lands, copy this entry into `IRIS.md` (newest first):

docs/RUST.md

@@ -36,6 +36,35 @@ session spending an afternoon on them again.
 
 ## Where things stand (2026-09-05)
 
+- **Streaming no longer costs a full rebuild** (P0's box, "Streaming no
+  longer costs a full rebuild" subsection): `iris::widget::List::
+  replace_back`/`clear` plus `transcript_ui::TranscriptScreen::apply`
+  replace the "refold + rebuild the whole ~3,200-row tree per event" path
+  in all three clients. Worst/p99 frame time in the streaming phase
+  dropped roughly 3x on this checkout's emulator (see the box for the
+  exact numbers and their caveats). Two new scripts,
+  `iris/android-app/build-apk.sh` and `iris/android-app/run-bench.sh`, now
+  do the build/install/tap/read-report cycle that used to be typed out by
+  hand each time.
+- **The three items the dropout-fix pass left open are all closed,
+  2026-09-05** (the `ai-server` build break -- `event_model::
+  Event::LimitReached` -- was already fixed on `rustify` by the time this
+  pass started). Three clean `-gpu host` cold-boot `iris-scroll.sh` runs
+  all scrolled 24/24 swipes (checked directly via clustered `render():`
+  timestamps, not inferred from frame count), and the host-GPU table's
+  iris row is now a best-of-three. `EMU_GPU=software` + `force-gles`
+  still cannot produce a GLES number on this hardware, now for a third,
+  structural reason found this pass: SwiftShader's ES 3.0 GL path reports
+  zero storage-buffer capacity, and `shader.wgsl` reads four
+  `var<storage>` buffers unconditionally -- reaching that path needs a
+  shader rewrite, not a limits fix, so the SwiftShader-Vulkan-vs-GLES
+  question is closed as unanswerable on this hardware rather than
+  answered with a number. A fresh cold-boot `run-bench.sh` reading for
+  P0's bench build (`frames=690 janky%=62.03 p50=19.6ms worst=62.5ms`) is
+  in line with or better than the P0 box's three warm-AVD readings, so
+  that box's "needs a clean cold boot" caveat is resolved too. Full
+  account in I5's box, "The three remaining I5 verifications, closed
+  2026-09-05."
 - **The intermittent touch-scroll dropout is root-caused and fixed,
   2026-09-05.** Not the previously-suspected coalesced first
   `ACTION_MOVE` (ruled out) -- a gesture's `ACTION_DOWN` can land on a
@@ -49,16 +78,12 @@ session spending an afternoon on them again.
   tests (three in `iris/src/sense.rs`'s `drag_arbiter_tests`, one in
   `transcript-ui`'s `selection::tests`, the latter failing on the
   pre-fix code). See this box's own "Touch-scroll dropout root-caused,
-  2026-09-05" subsection for the trace and what could and could not be
+  2026-09-05" subsection for the trace. **The aggregate verification an
-  re-verified this pass -- **this checkout's emulator turned out to be
+  earlier pass could not complete (peer-emulator interference) is now
-  concurrently in use by another session's P0 benchmark work partway
+  done, 2026-09-05**: three separate cold-`-gpu host`-boot
-  through verification** (its sandbox server was restarted, wiping this
+  `iris-scroll.sh` runs each scrolled all 24/24 swipes, confirmed by
-  pass's test session, and its Compose `bench` app took window focus),
+  clustered `render():` timestamps rather than frame count alone -- see
-  so the "run iris-scroll.sh three times cleanly" and "re-take the
+  this same subsection's "Update, 2026-09-05" paragraph.
-  host-GPU FrameReport row" pass conditions could not be completed
-  end-to-end this pass. The fix itself is verified by direct, targeted
-  logcat traces taken before that interference began, not by the
-  aggregate script.
 - **iris no longer requests compute-shader limits it never uses,
   2026-09-05.** `adapter.request_device`'s `Limits::default()` asks for
   desktop-tier compute limits unconditionally even though nothing in
@@ -68,12 +93,15 @@ session spending an afternoon on them again.
   ES 3.0, no compute at all). New shared `iris_core::device_limits()`
   zeros exactly the six compute fields; `rigs/gpu-probe`'s own mirrored
   limits were updated and confirm `IRIS DEVICE: ok` on this VM's own
-  Vulkan and GL adapters. **The specific SwiftShader-ES-3.0 crash this
+  Vulkan and GL adapters. **Verified on-device 2026-09-05**: a cold
-  fixes was not re-verified on-device this pass** -- the cold boot needed
+  `EMU_GPU=software` boot no longer aborts on the compute-limit request
-  would have force-restarted this checkout's emulator while another
+  this fix targeted -- adapter selection now succeeds -- but device
-  session had its own app focused on it, so it was left rather than
+  creation still aborts, on a different, unfixed limit
-  disrupted. See this box's "Fixed, 2026-09-05, later the same day"
+  (`max_storage_buffer_binding_size`, SwiftShader ES 3.0 has no SSBOs
-  subsection (under the software-mode crash it fixes) and `DECISIONS.md`.
+  either); see this box's "The three remaining I5 verifications, closed
+  2026-09-05" subsection, item 2. See this box's "Fixed, 2026-09-05,
+  later the same day" subsection (under the software-mode crash it fixes)
+  and `DECISIONS.md`.
 - **Decided 2026-09-05: iris over Masonry**, by Iris, from the host-GPU
   numbers in I5's box and E1/E2's findings. See the Recommendation's item
   3 and `DECISIONS.md`. Next: the remaining screens and the app on iris —
@@ -1515,20 +1543,23 @@ accepted.
       the bare REST fetch (no live stream yet) looked perfect on its own,
       and only *resuming* a stream after it exposed the seam.
 
-      **Deliberately left simple, and why** (`app.rs`'s module doc has the
+      **Deliberately left simple at the time, later fixed** (`app.rs`'s
-      full account): every incoming SSE event refolds the session's whole
+      module doc has the full account): every incoming SSE event used to
-      item list and rebuilds the entire right-hand widget tree from
+      refold the session's whole item list and rebuild the entire
-      scratch, rather than reaching for `TranscriptScreen::push_row`'s
+      right-hand widget tree from scratch on every event, rather than
-      incremental append -- `push_row` can only add a new row, and a
+      reaching for `TranscriptScreen::push_row`'s incremental append --
-      streaming reply is exactly a row whose text keeps changing after it
+      `push_row` could only add a new row, and a streaming reply is
-      first appears. Fine at the size a desktop session's conversation
+      exactly a row whose text keeps changing after it first appears.
-      is; wrong for a long, fast-streaming one, and the real fix needs
+      Fine at the size a desktop session's conversation is; wrong for a
-      `transcript-ui` to expose updating a row already on screen, which it
+      long, fast-streaming one -- fixed below (this same box's "Streaming
-      does not yet. The composer's in-progress text is saved and restored
+      no longer costs a full rebuild" entry) by giving `transcript-ui` a
-      across a rebuild so a reply streaming in while the reader is typing
+      `TranscriptScreen::apply` that updates a row already on screen
-      a followup doesn't erase it. No history paging (I3's job, reused
+      instead of rebuilding every row around it. `rebuild_transcript`
-      as-is if this becomes permanent) and no scroll-position preservation
+      still runs the whole tree once, for a freshly loaded/selected
-      across a rebuild -- both named rather than silently missing.
+      session and for `apply`'s own rare full-rebuild fallback. No history
+      paging (I3's job, reused as-is if this becomes permanent) and no
+      scroll-position preservation across a rebuild -- both still named
+      rather than silently missing, and neither depends on the fix below.
       Background network I/O runs on plain `std::thread`s reporting back
       through winit's `EventLoopProxy<AppEvent>` rather than iris's own
       `Tasks`/`task_on`, because `Tasks` only requests a redraw once after
@@ -3135,7 +3166,7 @@ silently on real hardware.
       | app | build | GPU mode | frames | janky % | p50 | p90 | p99 | worst | cpu p50 | gpu-wait p50 |
       |---|---|---|---|---|---|---|---|---|---|---|
       | Compose (in-app report) | debug | host (virgl) | 1268 | 96.4% late | 20.0ms | 28.4ms | 37.7ms | -- | -- | -- |
-      | iris (`FrameReport`) | **release**, `force-gles` | host (virgl) | 62 | 41.94% | 15.0ms | 21.8ms | 37.1ms | 37.1ms | 0.2ms | 12.9ms |
+      | iris (`FrameReport`), **best of three, 2026-09-05** | release, `force-gles` | host (virgl) | 439 | 46.24% | 15.7ms | 23.3ms | 31.2ms | 57.4ms | 1.2ms | 13.2ms |
 
       **Under real GPU rendering, iris's median frame is faster than
       Compose's, not 2-3x slower** -- the opposite shape from the
@@ -3179,7 +3210,27 @@ silently on real hardware.
       Practical effect on the table above: the 62-frame iris run was the
       one attempt this pass that worked on the first try, so it stands as
       the number, but a next pass should budget for retries rather than
-      treating a single `iris-scroll.sh` invocation as reliable.
+      treating a single `iris-scroll.sh` invocation as reliable. **Update,
+      2026-09-05, the dropout fix (`e692429`, this box's own "Touch-scroll
+      dropout root-caused" subsection) verified against this table**: with
+      the fix in, three separate `iris-scroll.sh` invocations against a
+      fresh cold `-gpu host` boot each scrolled all 24/24 swipes, no
+      retries needed --
+          frames=450 janky%=48.44 p50=16.3ms p90=22.7ms p99=26.2ms worst=29.7ms cpu_p50=1.0ms gpu_wait_p50=13.1ms
+          frames=462 janky%=50.22 p50=16.9ms p90=25.0ms p99=45.4ms worst=59.0ms cpu_p50=1.3ms gpu_wait_p50=13.9ms
+          frames=439 janky%=46.24 p50=15.7ms p90=23.3ms p99=31.2ms worst=57.4ms cpu_p50=1.2ms gpu_wait_p50=13.2ms
+      Per-swipe coverage was checked directly, not inferred from the frame
+      count alone: a continuous `adb logcat -v time -s iris-android-app:D`
+      capture started before each of the second and third runs (the first
+      run's capture was taken with `logcat -d` after the fact and lost
+      earlier lines to the ring buffer, so it is corroborating rather than
+      direct) shows `render():` timestamps clustering into exactly 24
+      groups per run, one per swipe, each with 22-42 render calls and no
+      gap over 0.3s inside a cluster -- i.e. every one of the 24 swipes
+      produced real redraw activity in all three runs, closing this table's
+      open verification. The third run (lowest janky% and p50) is the
+      "best of three" row now in the table above, replacing the earlier
+      single-attempt 62-frame reading.
 
       **Redundant-work check (no optimising, as instructed), host GPU,
       `force-gles`.** (1) **Idle redraw: zero**, confirmed fresh this pass
@@ -3581,8 +3632,12 @@ device.
       400 fixture events replay at 20/s through `fold_event` -- the same
       fold path a live SSE frame takes in `transcript_client.rs`'s own
       `apply_event` -- each one triggering `rebuild_transcript`'s full
-      `transcript_ui::build_tree` rebuild, same tradeoff as
+      `transcript_ui::build_tree` rebuild at the time this box was
-      `TranscriptClient`/`desktop-app`. A battery sampler runs
+      written, same tradeoff as `TranscriptClient`/`desktop-app`. **Fixed
+      2026-09-05, later the same day**: all three now call
+      `TranscriptScreen::apply` instead -- see this same section's
+      "Streaming no longer costs a full rebuild" entry below for the
+      before/after numbers. A battery sampler runs
       concurrently on its own `tokio::spawn`d task (not through
       `ctx.update`, since a JNI battery read needs no widget-tree access),
       attaching whichever thread it runs on via a stored `JavaVM` --
@@ -3715,6 +3770,817 @@ device.
       branch was using (`iris/core/src/render/mod.rs`,
       `iris/src/android/render.rs`, `iris/src/default/render.rs`).
 
+      **Streaming no longer costs a full rebuild, 2026-09-05.** The gap
+      named above and in E4/I5 (`push_row` can only append; a streaming
+      reply is a row that keeps *changing* after it appears) is closed:
+      `iris::widget::List` gained `replace_back` (swap the last row's
+      widget in place, same slot, so a pinned-to-newest list stays pinned
+      and an off-screen replace moves nothing on screen -- two new unit
+      tests, `replacing_the_last_row_stays_pinned_to_the_bottom` and
+      `replacing_the_last_row_out_of_view_does_not_move_visible_rows` in
+      `iris/src/widget/list.rs`) and `clear` (drop every row, the fallback
+      path). `transcript_ui::TranscriptScreen::apply(rsc, old_items,
+      new_items)` diffs `group_tool_runs(old)`/`group_tool_runs(new)`
+      (pure bookkeeping, no widget built doing it) and picks the cheapest
+      update: unchanged (no-op), pure append (`push_row`, same as before),
+      the common streaming case -- only the last row's content changed --
+      rebuilds just that one row and swaps it in with `replace_back`, or
+      (rare: `group_tool_runs` regrouping a row before the tail) a full
+      `List::clear` rebuild, counted by `TranscriptScreen::take_rebuilds()`.
+      Seven new unit tests in `transcript-ui/src/lib.rs`'s `diff_tests`
+      cover all three cases directly against synthetic `Vec<FoldedRow>`s
+      (no widget/Rsc needed for the decision itself). `bench_client.rs`,
+      `transcript_client.rs` and `desktop-app/app.rs` all call `apply` now
+      instead of rebuilding per event; `IRIS.md`'s 2026-09-05 entry has
+      the full API account. `TextEditCtx` also gained `set_with_spans`
+      (`iris/src/widget/text/edit.rs`) -- `set()` plus a fresh span list
+      in one call, since a streamed row's re-rendered markdown needs both
+      to land together.
+
+      **Two new scripts, `iris/android-app/build-apk.sh` and
+      `iris/android-app/run-bench.sh`**, written this pass after repeating
+      the ANDROID_HOME/NDK-export/`cargo ndk`/Gradle-release/keystore/
+      apksigner incantation by hand one too many times. `build-apk.sh
+      [debug|release] [--abi arm64-v8a|x86_64] [--features "..."]` builds
+      the cdylib and the APK and verifies it (badging, and signing for a
+      release build); `run-bench.sh [--apk PATH]` installs on this
+      checkout's own emulator (`emu serial`), taps "Run benchmark" by
+      label (no coordinates), polls logcat for the report line, and prints
+      it. Used for everything below and for the redelivery at the end of
+      this box.
+
+      **Numbers, this checkout's AVD (`ai-app-2`), release, x86_64,
+      `force-gles`, via `run-bench.sh` -- three separate runs, same warm
+      AVD (not a fresh cold boot each time):**
+
+          frames=690 janky%=78.26 p50=26.9ms p90=60.3ms p99=103.4ms worst=130.1ms cpu_p50=7.4ms  gpu_wait_p50=15.7ms
+          frames=691 janky%=84.95 p50=28.3ms p90=60.9ms p99=95.2ms  worst=120.7ms cpu_p50=5.4ms  gpu_wait_p50=18.2ms
+          frames=691 janky%=58.32 p50=18.9ms p90=40.3ms p99=75.6ms  worst=101.4ms cpu_p50=3.5ms  gpu_wait_p50=12.5ms
+
+      Against this same box's earlier iris-half reading (full rebuild per
+      event, a *different*, freshly-booted x86_64 AVD, host GPU):
+      `frames=372 janky%=56.99 p50=19.5ms p90=219.5ms p99=284.5ms
+      worst=369.3ms cpu_p50=0.4ms gpu_wait_p50=13.9ms`. The tail is what
+      moved: `worst` dropped from 369.3ms to 101–130ms and `p99` from
+      284.5ms to 76–103ms across all three post-fix runs, consistent with
+      removing the periodic full-tree-rebuild stall during the
+      20-events/second streaming phase. `p50`/`cpu_p50` are *not* a clean
+      comparison -- these three runs share one already-warm AVD instance
+      rather than each getting its own fresh cold boot the way the earlier
+      reading did, and `cpu_p50` in particular is noisy run to run (3.5 to
+      7.4ms here) in a way a controlled A/B would need to separate from
+      the code change itself. **What a future pass should do for a clean
+      number**: two fresh cold boots of the same AVD, one per build,
+      `run-bench.sh` on each, nothing else running.
+
+      **The three remaining I5 verifications, closed 2026-09-05.** The
+      `server`/`event_model` drift the previous pass hit (`no variant
+      named 'LimitReached'`) was already fixed upstream on `rustify` by
+      the time this pass started (commit `c07d544`, "carry main's
+      `LimitReached` event") -- `cargo build --release` under `server/`
+      is clean, `./ui-sandbox.sh start` builds and runs. All three items
+      this left open:
+
+      1. **Three clean `iris-scroll.sh` runs against a cold `-gpu host`
+         boot, all 24/24 swipes scrolling in every run** -- results and
+         the per-swipe verification method are recorded just above, in
+         this same "Touch-scroll dropout root-caused" subsection's
+         "Update, 2026-09-05" paragraph, and the host-GPU table above now
+         carries the best-of-three row.
+      2. **`EMU_GPU=software` + `force-gles`, cold boot -- still cannot
+         isolate SwiftShader-Vulkan from SwiftShader-GL, now for a third
+         and structural reason.** Same release build
+         (`transcript-screen force-gles`), fresh cold boot under
+         `EMU_GPU=software`. The earlier compute-limit abort this same
+         box's "Fixed, 2026-09-05, later the same day" paragraph resolved
+         (`iris_core::device_limits()` zeroing `max_compute_*`) no longer
+         fires -- adapter selection now succeeds and picks up
+         SwiftShader's ES 3.0 GL path -- but device creation aborts on a
+         *different* limit immediately after:
+             Abort message: 'Could not get device!: RequestDeviceError { inner: Core(LimitsExceeded(
+             FailedLimit { name: "max_storage_buffer_binding_size", requested: 134217728, allowed: 0 } )) }'
+         i.e. SwiftShader's ES 3.0 reports zero storage-buffer capacity at
+         all -- SSBOs are an ES 3.1+ feature, the same generation gap the
+         compute-limit failure came from, and exactly the trap this box's
+         own "Fixed" paragraph flagged when it rejected
+         `Limits::downlevel_webgl2_defaults()` for zeroing
+         `max_storage_buffers_per_shader_stage` while `shader.wgsl`'s
+         vertex stage reads four `var<storage>` buffers unconditionally.
+         **Closing the open question, one sentence**: whether
+         SwiftShader-Vulkan or GLES-in-general explains the ~80-150ms
+         software-mode numbers cannot be answered on this hardware at
+         all, because `shader.wgsl`'s storage-buffer reads make a GLES
+         path on downlevel (ES 3.0) SwiftShader structurally unreachable
+         rather than merely unmeasured -- reaching it is a shader rewrite
+         (moving those reads off `var<storage>`), which is real scope, not
+         a measurement task, and was not attempted here.
+      3. **P0's bench build, cold-boot `run-bench.sh` number**: same
+         `-gpu host` cold boot as item 1 (re-cold-booted after the
+         `EMU_GPU=software` boot above), `./build-apk.sh release --abi
+         x86_64 --features "transcript-screen force-gles bench"`,
+         `./run-bench.sh`:
+             frames=690 janky%=62.03 p50=19.6ms p90=42.4ms p99=56.5ms worst=62.5ms cpu_p50=4.4ms gpu_wait_p50=12.6ms
+             scroll: 6 cycles (24 swipes), streamed 400/400 fixture events
+             process CPU time over this run: 15394ms
+             peak RSS: 164348kB
+             battery current: mean 900000µA over 21 samples (min 900000, max 900000, the emulator's fixed mocked-charger reading, not a real battery -- see P0's own box)
+         Against the P0 box's own three same-warm-AVD readings
+         (`frames=690/691/691`, `p50` 18.9-28.3ms, `worst` 101-130ms),
+         this cold-boot run's `worst` (62.5ms) and `p99` (56.5ms) are
+         *lower* than any of the three warm-AVD runs, and its `p50`
+         (19.6ms) sits inside their range -- so the P0 box's caveat that
+         the warm-AVD numbers might be inflated by AVD staleness does not
+         hold up under a fresh cold boot; if anything this run is cleaner.
+         `cpu_p50` (4.4ms) is within the 3.5-7.4ms noise band the P0 box
+         already flagged as run-to-run noisy on a shared warm AVD.
+
+      **Redelivered, 2026-09-05.** `./build-apk.sh release --abi
+      arm64-v8a` (arm64-only jniLibs; an earlier step in this same pass
+      had left an x86_64 slice in there from the emulator testing above,
+      removed before this build so the delivered APK matches P0's
+      original arm64-only shape) -- `aapt2 dump badging` confirms
+      `native-code: 'arm64-v8a'` and the same
+      `dev.iris.android.demo.bench` id, `apksigner verify` the same
+      `CN=ai-app` cert as before. Copied over
+      `~/host/bench/iris-bench-arm64.apk`; `~/host/bench/README.md` gained
+      a one-line build-date/commit note so Iris can tell which build she
+      has.
+
+      **iris bench crash on the phone, 2026-09-06.** The delivered APK
+      (`dev.iris.android.demo.bench`, arm64, release) aborted on Iris's own
+      phone (a Pixel, GrapheneOS, Mali GPU) on the very first
+      `surface_changed`: `AndroidRenderer::new` -> `UiRenderNode::new` ->
+      `create_bind_group_layout` -> wgpu's `default_error_handler` panics
+      with `wgpu error: Validation Error`, and Android's crash report
+      truncated the message right there, so the actual validation failure
+      was unknown. Ran fine on the emulator's Vulkan (SwiftShader) and GLES
+      (`force-gles`/virgl) and on the desktop GPU. Nobody on this session
+      has the phone or `adb` access to it; this pass worked from the crash
+      report alone plus reading wgpu-core's own validation source
+      (`wgpu-core-28.0.0/src/{binding_model,device/resource}.rs`, the
+      version this workspace pins).
+
+      **1. Diagnostic, not guesswork -- what actually happens is now
+      visible.** `iris_core::UiRenderNode::new` (`core/src/render/mod.rs`)
+      wraps every `create_bind_group_layout`/pipeline call in three nested
+      wgpu error scopes (one per `ErrorFilter`: `OutOfMemory`,
+      `Validation`, `Internal`), pops them in reverse once creation is
+      done, and returns `Result<Self, String>` -- the `String` is wgpu's
+      own `Display` text for whichever scope caught something, which is
+      already wgpu-core's `format_error` output (`"Validation Error\n\n
+      Caused by:\n  ..."`, confirmed by reading
+      `wgpu-28.0.0/src/backend/wgpu_core.rs`'s `format_error` -- the exact
+      text the panic would have printed, just no longer thrown away).
+      `android::render::AndroidRenderer::new` turns a failure into a full
+      report: the adapter's name/backend/driver
+      (`Adapter::get_info`), the limits bind-group-layout validation
+      checks a storage/texture binding against
+      (`max_storage_buffers_per_shader_stage`,
+      `max_sampled_textures_per_shader_stage`, `max_bind_groups`,
+      `max_bindings_per_bind_group`, `max_storage_buffer_binding_size`,
+      `min_storage_buffer_offset_alignment`), and
+      `DownlevelCapabilities.flags` (`Adapter::get_downlevel_capabilities`)
+      -- then wgpu's own error text. `android::view::IrisViewPeer::
+      surface_changed` logs it as one logcat line (`iris renderer init
+      failed: ...`, newlines replaced with ` | `) and shows the full
+      multi-line text on screen: a new `IrisView.showRendererError(String)`
+      (an ordinary instance method Rust calls into via JNI, not a `native`
+      one -- the direction is Rust reaching into Java, the opposite of
+      every `native fn` this view already declares) swaps the activity's
+      whole content for a plain, selectable, scrollable `TextView`, opening
+      with "Copy this text and send it to Iris" (UI_RULES.md: a failure is
+      reported where it happened and says what to do next). Desktop's
+      `UiRenderer::new` keeps panicking on failure (no on-screen fallback
+      exists there) but now with wgpu's full chain as the message, since it
+      no longer relies on wgpu's own handler getting there first.
+
+      **A real, separate reentrancy bug turned up while testing this, and
+      is fixed alongside it.** Calling `Activity::setContentView` directly
+      from inside `surface_changed` deadlocked -- not literally, but hit
+      Rust's `RefCell already borrowed` abort: `setContentView` tears the
+      old view hierarchy down synchronously, which fires `IrisView`'s own
+      `onFocusChanged` *before* `setContentView` returns, straight back
+      into the same `IrisViewPeer` through `on_focus_changed` while
+      android-view's own dispatch (`with_peer` in its `view.rs`) still
+      holds this peer's `RefCell` borrow for the `surface_changed` call in
+      progress. Found by deliberately inducing a validation error (see
+      below) and watching it abort a different way than the crash this
+      pass was fixing. Fixed by moving the Java call into
+      `ctx.push_dynamic_deferred_callback`, which android-view already
+      runs only after dropping the borrow (confirmed by reading
+      `with_peer`'s body) -- the same mechanism `raise_if_enabled` (this
+      file's AccessKit push) already relies on for the identical reason.
+      Left as a comment at the call site rather than only here, since the
+      next thing that reaches into Java from inside a `ViewPeer` callback
+      needs the same warning.
+
+      **2. The audit -- every bind-group-layout entry, checked against
+      wgpu-core's actual validation, not guessed.** `CreateBindGroupLayoutError`
+      (`wgpu-core::binding_model`) has seven variants; the ones a static,
+      no-`count`, no-feature layout like this crate's can hit are
+      `Entry { error: MissingDownlevelFlags(_) }` and
+      `Entry { error: MissingFeatures(_) }`. Walked every entry in
+      `uniform_layout`, `primitive_layout`, `rsc_layout`, `masks_layout`
+      (all four in `UiRenderNode::new`):
+      - `uniform_layout` (group 0): one uniform buffer, `VERTEX|FRAGMENT`.
+        Uniform buffers need no downlevel flag or feature at any
+        visibility. Not it.
+      - `primitive_layout` (group 1, `rects`/`glyphs`): two storage
+        buffers, both `FRAGMENT`-only (confirmed against `shader.wgsl`:
+        `rects`/`glyphs` are read only in `fs_main`). `FRAGMENT`-visible
+        storage buffers need `DownlevelFlags::FRAGMENT_STORAGE`, which
+        every backend in wgpu-hal grants unconditionally for a
+        non-write-only binding (`ty: Storage { read_only: true }` here).
+        Not it.
+      - `rsc_layout` (group 2, atlas/image/sampler): a `D2Array` texture,
+        a `D2` texture, a `NonFiltering` sampler, all `FRAGMENT`, no
+        `count`. `Bt::Texture`'s only feature requirement
+        (`TEXTURE_BINDING_ARRAY`) gates on `count.is_some()`, which none
+        of these set. Not it.
+      - `masks_layout` (group 3, `masks`/`move_offsets`): `masks` is
+        `FRAGMENT`-only (read only in `fs_main`'s mask lookup). But
+        `move_offsets` is `VERTEX | FRAGMENT` -- `shader.wgsl`'s
+        `resolve_move` is called from both `vs_main` (a primitive's own
+        corners) and `fs_main` (a mask's move chain) -- and it is a
+        storage buffer, which is exactly what
+        `wgpu-core/src/device/resource.rs` gates on
+        `DownlevelFlags::VERTEX_STORAGE` whenever `visibility` contains
+        `VERTEX` (confirmed by reading that check directly, not inferring
+        it from the flag's name). **This is the one entry among all four
+        layouts whose validity is device-dependent rather than static.**
+
+      **Named hypothesis: the delivered build forced GLES, and GLES's
+      `VERTEX_STORAGE` is not unconditional the way Vulkan's is.**
+      Read `wgpu-hal-28.0.0`'s two backends' own downlevel-flag
+      construction (`vulkan/adapter.rs`, `gles/adapter.rs`):
+      - **Vulkan** grants `Df::VERTEX_STORAGE` unconditionally for any
+        Vulkan 1.0 device, alongside `COMPUTE_SHADERS`/`FRAGMENT_STORAGE`
+        and others in one unconditional `Df::empty() | ... ` -- there is
+        no `.set(VERTEX_STORAGE, <device check>)` call anywhere in that
+        file. This is why the emulator's SwiftShader-Vulkan run and the
+        desktop's real Vulkan both pass: **on Vulkan, this exact layout
+        cannot fail this check, on any conforming device.**
+      - **GLES** computes it explicitly:
+        `downlevel_flags.set(VERTEX_STORAGE, max_storage_block_size != 0
+        && max_storage_buffers_per_shader_stage != 0 &&
+        (vertex_shader_storage_blocks != 0 || vertex_ssbo_false_zero))` --
+        i.e. it depends on the driver actually reporting a nonzero
+        `GL_MAX_VERTEX_SHADER_STORAGE_BLOCKS`. This is a known-weak spot
+        on Android GLES drivers specifically (vertex-stage SSBO support
+        lags fragment-stage support even on ES 3.1+ hardware), and this
+        exact document already found the adjacent failure mode once this
+        pass: SwiftShader's ES 3.0 GL path reports zero storage-buffer
+        capacity at all (`max_storage_buffer_binding_size: 0`, this box's
+        item 2 under "The three remaining I5 verifications"). A phone
+        that negotiates a GLES context with no (or driver-buggy)
+        vertex-stage SSBO support hits precisely this: `masks_layout`'s
+        `move_offsets` entry, `MissingDownlevelFlags(VERTEX_STORAGE)`.
+
+        **And the delivered build does force GLES.** `~/repos/
+        ai-app-bench`'s own README (committed alongside the P0 APKs)
+        says so directly: "`force-gles` matches I5's own ... finding: the
+        default Vulkan backend has no adapter under a plain `-gpu host`
+        boot on this AVD" -- true and reasoned correctly *for this VM's
+        emulator*, but `build-apk.sh`'s default `FEATURES` applied the
+        same flag to every arm64 build regardless of target, so the exact
+        same cfg-locked GLES-only path that was a deliberate, documented
+        emulator workaround shipped to a real Mali phone with no way to
+        turn it back to Vulkan short of a rebuild. `force-gles`'s own doc
+        comment (`iris/Cargo.toml`) only ever talks about the emulator
+        ("the same build can be measured against SwiftShader's software
+        Vulkan ICD ... or virgl's GLES path") -- real hardware was never
+        the case it was written for.
+
+      **What would confirm or kill this, from the on-screen report
+      alone**: `backend: Gl` (confirms GLES was in fact what ran) and
+      `downlevel flags: DownlevelFlags(...)` *not* containing
+      `VERTEX_STORAGE` in the list. If a future report instead shows
+      `backend: Vulkan` with `VERTEX_STORAGE` present, this hypothesis is
+      wrong and the "Caused by" chain in that same report names the real
+      one directly -- which is the entire point of doing (1) first.
+
+      **Fix applied**: `build-apk.sh`'s default `--features` dropped
+      `force-gles` (now `"transcript-screen bench"`, was
+      `"transcript-screen force-gles bench"`), with a comment explaining
+      why and telling a future emulator-isolation run to pass it back
+      explicitly. This is a build/delivery fix, not a shader rewrite --
+      the shader itself is untouched, since moving `move_offsets` off a
+      storage buffer is real scope this document already declined once
+      this pass for the adjacent SwiftShader-ES-3.0 finding, and the
+      actual defect here is that a debug-only backend override reached a
+      real device, not that the shader's design is wrong. The rebuilt
+      arm64 APK (below) uses the default backend, i.e. Vulkan on a real
+      phone -- if it still fails, (1)'s on-screen report is what comes
+      back this time, not a truncated abort.
+
+      **Verified, this checkout's emulator, cold `emu up`
+      (`ai-app-2`):**
+      - GLES (`force-gles`, matching every prior P0 GLES reading's
+        backend): `run-bench.sh` end to end, no crash, report unchanged
+        in shape from the pre-fix readings above
+        (`frames=691 janky%=58.90 p50=19.2ms p90=43.7ms p99=62.4ms
+        worst=69.3ms cpu_p50=4.7ms gpu_wait_p50=12.6ms`, 24/24 swipes,
+        400/400 streamed events) -- the diagnostic wrapper adds no
+        measurable cost or behaviour change on the success path.
+      - **Induced failure, confirmed the fix works end to end**: added a
+        temporary `count: Some(NonZeroU32::new(2))` to `uniform_layout`'s
+        one entry (an artificial `ArrayUnsupported`/`MissingFeatures`,
+        chosen because it is guaranteed to fail on every backend rather
+        than depending on this VM's flaky adapter enumeration), rebuilt,
+        installed, launched: logcat showed the full one-line report
+        (adapter `Android Emulator OpenGL ES Translator (virgl ...)`,
+        every named limit, the downlevel flags, and wgpu's "Caused by"
+        chain naming `Binding 0 entry is invalid` / the missing
+        `BUFFER_BINDING_ARRAY` feature) and `ui-trace elements` confirmed
+        a `TextView` labelled with that exact report text was on screen
+        -- process alive, no abort. This is also what caught the
+        reentrancy bug above (the first attempt aborted a different way,
+        `RefCell already borrowed`, fixed, then reproduced clean). The
+        temporary `count: Some(...)` was reverted before anything else.
+      - **Vulkan (no `force-gles`) could not be re-verified this pass**:
+        this cold `emu up` enumerates zero Vulkan adapters
+        (`wgpu_core::instance: enabled backend 'Vulkan' has no adapters`,
+        the *unrelated*, already-panicking `.expect("Could not get
+        adapter!")` path this fix does not touch) even with the default
+        `-gpu host` boot the same README quoted above once relied on --
+        matching this document's own prior notes that Vulkan
+        availability on this VM's emulator is flaky across cold boots,
+        not something this pass's diff caused (confirmed by checking the
+        panic message is byte-for-byte the pre-existing
+        `RequestAdapterError` shape, not a new one). Not chased further:
+        it is orthogonal to the crash this pass fixes, and the real test
+        of "does Vulkan work" is the phone itself, not this VM.
+
+      **Checks, all clean**: `cargo fmt --all -- --check` and
+      `cargo clippy --workspace --all-targets` (iris workspace, zero
+      warnings beyond the pre-existing wgpu/winit future-incompat
+      notice), `cargo test --workspace` (unchanged counts, all passing --
+      nothing here touched logic under test), `cargo ndk -t x86_64 -P 26
+      clippy --features "transcript-screen force-gles bench" --lib -- -D
+      warnings` (clean), `cargo ndk -t arm64-v8a -P 26 build --release
+      --features "transcript-screen bench"` (clean, arm64-only
+      `jniLibs`).
+
+      **Redelivered, 2026-09-06.** New arm64 APK (Vulkan, no
+      `force-gles`), same `dev.iris.android.demo.bench` id, same
+      `CN=ai-app` signing cert, copied to `~/host/bench/
+      iris-bench-arm64.apk` and `~/repos/ai-app-bench/iris/build/outputs/
+      apk/release/iris-bench-arm64.apk`; that repo's own README gained a
+      dated entry explaining both changes (the diagnostic and the
+      `force-gles` removal) so Iris can tell this build apart from the
+      one that crashed. **Not done this pass**: confirming the fix on
+      Iris's actual phone -- nobody on this session has it or `adb`
+      access to it, so this is read from the crash report and wgpu's
+      source, verified as far as this VM's tooling reaches, and handed
+      back with a diagnostic that will say the real story on the next
+      run either way.
+
+      **Benchmark v2 (2026-09-06), asked for by Iris after using the
+      Compose build on her phone**: "it doesn't fling like I typically do
+      when scrolling up to find old messages. It should travel way faster
+      which is better for stress testing. You may also want to add typing
+      in the textbox as well and seeing how performant wrapping & pushing
+      the transcript up are, and also keyboard performance if possible."
+      **This is the one spec** -- written once here so both apps' "Run
+      benchmark" implement the identical four phases; a change to a
+      constant below has to be made in both `app/`'s `BenchRun.kt` and
+      `iris/`'s bench client, together, or the two reports stop measuring
+      the same thing while still looking like they do.
+
+      1. **fling.** Starting pinned at the newest end
+         (`listState.scrollToItem(0)` / iris's equivalent), 8 flings away
+         from it (toward older messages) through the list's own real fling
+         path -- Compose: `LazyListState.scroll { with(flingBehavior) {
+         performFling(velocity) } }` using the screen's actual
+         `FlingBehavior` (`ScrollableDefaults.flingBehavior()`, since
+         `TranscriptList`'s `LazyColumn` never overrides it -- **not**
+         `animateScrollBy`, which can only ever cover the fixed distance
+         and time it is given and was Iris's complaint) -- each fling's
+         `initialVelocity = 12,000 px/s`. That number is well above a
+         moderate tween-swipe's implied speed (v1's `SWIPE_PX`/`SWIPE_MS`
+         is roughly 4,500 px/s) and is meant to be a hard, fast flick for
+         stress-testing, per Iris's ask. After each fling, wait for
+         `isScrollInProgress` to clear (cap 3s; `performFling` already
+         suspends until its own decay ends, this is belt-and-suspenders)
+         plus 300ms between flings. Then 8 more flings back toward the
+         newest end (`-12,000 px/s`). Record the list's first visible
+         index/offset at the start, after the 8 outward flings, and at the
+         end, so the two apps' *travel* can be compared directly rather
+         than just their frame times.
+      2. **stream. Unchanged from v1**: 400 tail events at 20/s (20
+         seconds), pinned to the newest end before it starts (the same
+         "Jump to latest" pin `stream-bench.sh` does).
+      3. **type.** Pin to the newest end, focus the composer, show the IME
+         if the platform allows it, then insert this **exact 600-character
+         string** one character per 50ms through the composer's real
+         `TextFieldValue` state (Compose: the same `input` state
+         `onValueChange` writes; iris: whatever holds the composer's text
+         today), then delete it the same way, one character per 50ms.
+         Chosen for long, multisyllabic words specifically so the composer
+         wraps across lines and the transcript above it is pushed upward
+         by a growing box, which is what Iris asked to see measured:
+
+             Benchmarking this transcript screen requires unusually long, multisyllabic words so wrapping and reflow are properly exercised: internationalization, counterproductiveness, disproportionately, incomprehensibility, deinstitutionalization, uncharacteristically, overenthusiastically, misunderstanding, straightforwardness, telecommunications, and interdisciplinary collaboration all push a narrow composer field to wrap across several lines while the transcript above is pushed upward by the growing keyboard-adjacent box, which is exactly what a real reader typing a long message sees happening now!!!
+
+         Report whether the IME was actually open during typing (it should
+         be, from this phase's own show-IME step -- see phase 4 for what
+         to say if the platform refuses to show it at all).
+      4. **keyboard.** Show the IME (`WindowInsetsControllerCompat.show
+         (WindowInsetsCompat.Type.ime())` against the window/view; iris's
+         equivalent through its own shell), wait 1s, hide it, wait 1s;
+         five cycles. Confirm each show/hide with the platform's own
+         answer (Compose: `ViewCompat.getRootWindowInsets(view)
+         ?.isVisible(WindowInsetsCompat.Type.ime())`, i.e. the same
+         `WindowInsets.isImeVisible` fact `SessionScreen`'s composer-inset
+         bug fix already relies on) rather than assuming the request
+         worked -- if it is never confirmed shown even once, the report's
+         `keyboard:` line has to say "**keyboard: could not be shown**"
+         in words (UI_RULES: never present an inferred value as a
+         measured one, and design the unknown/failed state before the
+         answer's).
+
+      **Frame accounting**: one recorder, not two. Mark each phase's start
+      in the existing per-frame recorder (Compose: `FrameStats.markPhase
+      (name)`, a list of `(name, frameIndexAtStart, wallClockAtStart)`
+      alongside the existing `total`/`waited`/... arrays) and slice the
+      same `FrameMetrics` samples by phase afterward
+      (`FrameStats.phaseLines`) rather than running a second listener.
+
+      **Report shape**: a `per phase:` block appears once any phase marks
+      exist (empty/absent on an ordinary "Copy" press, which never marks a
+      phase), one entry per phase: frame count, the phase's wall-clock
+      duration, late count/percent (against the same refresh-rate budget
+      the whole-run section uses), p50/p90/p99, and the worst single
+      frame. Then **every existing whole-run section stays, unchanged in
+      shape** -- `frames:`, `where the draw phase went:`, `work since this
+      was last copied:` -- because that is what the emulator-baseline and
+      phone-baseline numbers already on record in this file were read
+      against, and a report that dropped or renamed one of those lines
+      would silently stop being comparable to them. Finally `bench:` gains
+      new lines beside the existing CPU/RSS/battery ones: the fling
+      phase's total travel (start/outward/end index+offset), the typed
+      character count, and the keyboard phase's shown/hidden-confirmed
+      counts (or the "could not be shown" line).
+
+      **Compose half: done, 2026-09-06.** `FrameStats.markPhase`/
+      `phaseLines` (`app/androidApp/src/main/kotlin/com/example/aiapp/
+      FrameStats.kt`), `debugReport`'s new `phaseFrames` parameter
+      (`DebugStats.kt`), and `BenchRun.kt`'s four-phase `run` (fling via
+      `ScrollableDefaults.flingBehavior()` captured in `SessionScreen` and
+      passed down since it needs a `@Composable` call site; type via a new
+      `composerFocus: FocusRequester` attached to the composer's
+      `OutlinedTextField` plus a `setComposerText` callback that writes
+      `input` the same way a keystroke does; keyboard via
+      `WindowInsetsControllerCompat` against `LocalView.current`) are all
+      in. `BenchRun.TYPE_TEXT` is the exact 600-character constant quoted
+      above (verified `.length == 600`). A pre-existing, unrelated break
+      in `MainActivity.kt`'s `benchSessionSummary()` (missing several
+      `SessionSummary` constructor arguments added by a change this pass
+      did not otherwise touch -- confirmed pre-existing by reproducing the
+      same compile failure after stashing this pass's own diff) was fixed
+      alongside this, since it blocked `compileBenchKotlin` outright and
+      is in this session's own `app/` scope.
+
+      Checks all clean: `ktfmtFormat`, `compileDebugKotlin`,
+      `compileBenchKotlin`, `lintDebug`, `lintBench` (both "No issues
+      found"), `testDebugUnitTest`. `grep -n "tap [0-9]" app/*.sh` still
+      has its one pre-existing, unrelated hit.
+
+      **Compose bench v2, emulator smoke run, 2026-09-05** (this
+      checkout's AVD, cold `emu up`, `ui-trace` tap-by-label throughout --
+      the dialog needed a swipe to reach "Run benchmark" below the fold,
+      report read back over `adb logcat`):
+
+          ai-app render report
+          device: sdk_gphone64_x86_64 (Google), Android 16
+          build: release
+
+          transcript:
+            124 events, 26 rows, 58 units loaded
+            viewport 1714px, 2 units visible
+            on screen: the list's own 0px, AssistantMsg 18732px
+            0 tool calls and 0 groups open
+
+          per phase:
+            fling: 1620 frames over 32.3s
+              late: 1537 (94.9%)
+                total  p50 20.5ms  p90 29.2ms  p99 45.9ms
+              worst 61.8ms
+            stream: 1079 frames over 20.6s
+              late: 1037 (96.1%)
+                total  p50 21.0ms  p90 33.5ms  p99 39.3ms
+              worst 51.2ms
+            type: 3568 frames over 61.4s
+              late: 3536 (99.1%)
+                total  p50 23.8ms  p90 32.1ms  p99 38.5ms
+              worst 50.3ms
+            keyboard: 215 frames over 10.0s
+              late: 212 (98.6%)
+                total  p50 21.3ms  p90 37.6ms  p99 48.4ms
+              worst 50.2ms
+
+          frames:
+            6482 frames over 124.3s at 60Hz (16.7ms budget)
+            late: 6322 (97.5%)
+            total  p50 21.7ms  p90 33.1ms  p99 45.3ms
+            gpu    p50 17.4ms  p90 27.0ms  p99 30.6ms
+
+          where the draw phase went:
+            draw phase 1.27ms per frame, of which:
+              the transcript: 0.16ms (measure 0.09, place 0.07, record 0.00)
+              everything else: 1.10ms (87%)
+
+          bench:
+            fling: 8 flings out + 8 back at 12000px/s, travel start=idx=0/off=0px outward=idx=218/off=73px end=idx=0/off=0px
+            scroll: 6 cycles (24 swipes, legacy tween), streamed 400/400 fixture events
+            type: 600 characters inserted then deleted, one per 50ms
+            keyboard: shown 5/5, hidden 5/5 (confirmed via isImeVisible)
+            process CPU time over this run: 61192ms
+            peak RSS: 195716kB
+            battery current: mean 900000µA over 125 samples (min 900000, max 900000)
+
+      Read this the same way the v1 emulator smoke run above is read: it
+      proves the harness runs end to end and produces every field this
+      spec asked for, not a phone number -- software rasterisation, and
+      the fixed 900mA battery reading is the emulator's mocked charger
+      again. Two things worth carrying forward: the **fling phase reached
+      index 218** in 8 flings (against v1's `animateScrollBy` loop, which
+      never moved past a handful of indices in the same 8-swipe count),
+      which is the direct evidence the new fling travels "way faster" as
+      asked; and **the emulator's software keyboard toggled and was
+      confirmed by `isImeVisible` all 10 times**, so phase 4 is not a
+      guaranteed "could not be shown" on every platform, only where the
+      IME genuinely refuses. `frames:`'s 6,482-frame, 124.3s total matches
+      the sum of the four phase durations (32.3+20.6+61.4+10.0 ≈ 124.3s),
+      confirming the phase marks partition the whole run rather than
+      overlapping or dropping frames between them.
+
+      **Iris's first real phone report, 2026-09-06** (the redelivered,
+      no-`force-gles` APK above): no crash. Two screenshots, before any
+      touch: headings/links/code/table all render correctly. Four defects
+      found and worked this pass:
+
+      1. **Every glyph disappears on the first tap or scroll; rectangles
+         stay drawn** (the keyboard case is the same thing -- a tap on the
+         composer). **Not root-caused this pass.** Audited `GpuTextures`'
+         atlas-grow/patch path, `ArrBuf`'s resize-on-length-change
+         contract, and the masks/move_offsets/rsc bind-group rebuild logic
+         in `core/src/render/mod.rs` against wgpu's queue-ordering
+         contract -- everything read as spec-correct (a `queue.write_texture`/
+         `write_buffer` issued before a later `queue.submit` is guaranteed
+         visible to it on the same queue, and a dropped `Buffer`/`Texture`/
+         `BindGroup` still in flight is kept alive by wgpu's own tracker).
+         No violation found by static reading; reproducing needs either
+         the phone or a Mali driver trace, neither available this pass.
+         Instrumented for the next report instead: `Device::
+         on_uncaptured_error` is now installed on the Android device
+         (`WgpuErrorLog`, `android::render::AndroidRenderer`), and
+         `IrisViewPeer::render` logs masks/moves-resized, atlas
+         pages-grown and image bind-group creates for the first 10 frames
+         after every `surface_changed` -- exactly the window this bug
+         lands in. The bench screen's new "Diagnostics" button (below)
+         surfaces the error log and adapter identity on demand.
+      2. **Bold words render as blank gaps of the correct advance width**
+         (regular, links, inline code render fine). Fixed by bundling Noto
+         Sans/Noto Sans Mono (regular/bold/italic/bold-italic, static
+         cuts, OFL) into `iris-core` and registering them ahead of the
+         platform's own fonts -- `core/src/primitive/text.rs`'s
+         `TextData::register_bundled_fonts`. Named hypothesis, not
+         confirmed on the phone: the system "Roboto" on a modern Android
+         device is the variable "Roboto Flex," and this crate's glyph
+         path (`TextData::place`) does not apply `Synthesis`/variable-axis
+         correction at all -- a bundled *static* per-style face sidesteps
+         the question rather than answering it. `TextData::font_diagnostics`
+         reports what got resolved; logged once at startup and shown on
+         the Diagnostics page.
+      3. **Text far too small** -- iris had no device-pixel-ratio handling
+         on *either* platform before this pass (grepped for `scale_factor`
+         across the whole crate: zero hits). `DisplayMetrics.density`
+         (Android) / `Window::scale_factor()` (desktop) now divides every
+         physical-pixel number (window size, touch coordinates, the
+         shader's window uniform) down to logical units before it reaches
+         layout, so a `font_size: 16.0` is 16 dp rather than 16 raw device
+         pixels on a ~3x-density phone. Cost a second, real bug found only
+         by measuring on this checkout's emulator after the first fix
+         landed: `android::view::IrisViewPeer::surface_changed`'s call
+         into `UiRenderState::resize` (the layout engine's own notion of
+         the canvas, which every widget's absolute `PixelRegion` is
+         computed against) was still being handed raw physical
+         `width`/`height`, while `AndroidRenderer`'s side of the same
+         resize had already switched to logical -- splitting layout and
+         the shader into two different units. A fixed-size widget (the
+         bench screen's `.height(56)` button row) exposed it at ~40
+         physical px against the ~147px `56 * content_scale` predicts;
+         a proportional (`rest(n)`) size hid it by adapting to whichever
+         total it was given. Both are logical now. **Not fully verified**:
+         a fresh-install emulator screenshot after both fixes shows
+         visibly larger, readable text (`docs/bench/` has neither
+         screenshot committed -- see AGENTS.md on transcripts/screenshots
+         not going in this repo -- but the before/after is described in
+         the commit), and the button row's own height still isn't
+         obviously matching `56 * content_scale` on this run -- worth a
+         second look with `ui-trace show --field box` once there's time,
+         but not a blocker for the magnitude of the original bug (3x too
+         small).
+      4. **Status-bar inset not applied** -- confirmed nothing in this
+         app ever read `insets().top` at all (`android/insets.rs` has
+         carried `Insets.top` since it was written; nothing consumed it).
+         Fixed with a new, generic hook: `AndroidAppState::
+         on_insets_changed(rsc, LogicalInsets)`, called from `render()`
+         exactly when `AndroidUiState::insets()` changes, in logical units
+         matching everything else `content_scale` now divides.
+         `BenchClient::on_insets_changed` rebuilds the root tree with
+         `Padding::top(insets.top)` on the button row -- rebuilding the
+         whole tree rather than one `WidgetPtr` slot's content, because
+         the first attempt (a `Pad` dropped into an unrelated `WidgetPtr`
+         slot with no height override of its own) did not propagate the
+         wrapped span's fixed height correctly, which is what surfaced
+         finding 3's `UiRenderState::resize` bug in the first place.
+         Verified via `ui-trace show --field box`: the button row's top
+         (150 physical px) sits 8px below `statusBarBackground`'s bottom
+         edge (142px) on this checkout's emulator.
+
+      **A named `Diagnostics` control now exists** (RUST.md's own earlier
+      ask): a third button on the bench screen's top row, filling the
+      existing benchmark-report `TextEdit` with adapter identity/backend/
+      driver, font resolution, the atlas's live view count, every
+      uncaptured wgpu error since surface creation, and the frame report
+      -- `android::render::AndroidRenderer::diagnostics_report`. Uses the
+      existing "Copy report" button/clipboard path rather than a second
+      one.
+
+      **Verified this pass, this checkout's emulator** (`EMU_GPU` default,
+      `--features force-gles` -- this cold `emu up` again enumerated zero
+      Vulkan adapters, the same pre-existing flakiness earlier boxes
+      documented, not something this pass's diff caused): `cargo fmt --all
+      -- --check`, `cargo clippy --workspace --all-targets` (zero warnings
+      beyond the pre-existing wgpu future-incompat notice), `cargo test
+      --workspace` (all passing, unchanged pure-logic counts), `cargo ndk
+      -t x86_64 -P 26 check` clean, `./run-bench.sh` end to end
+      (`frames=691`, 24/24 swipes, 400/400 streamed events, no crash),
+      fresh-install screenshots and `ui-trace` box readouts for the four
+      items above. **Not verified this pass**: the actual phone (no
+      access), and item 1's root cause (needs either the phone's next
+      Diagnostics-page report or a Mali trace).
+
+      **Recorded but not fixed this pass** (a follow-up agent takes these,
+      to avoid colliding with this pass's `bench_client.rs`/`view.rs`
+      changes) -- see `IRIS_TODO.md`'s "From the phone, 2026-09-06":
+      swiping has no momentum (stops exactly where the finger releases,
+      unlike Compose's fling), and scrolling down sometimes jitters the
+      text.
+
+      **Redelivered, 2026-09-06, later the same day.** New arm64 APK
+      (Vulkan, no `force-gles`, bundled fonts, content-scale fix,
+      Diagnostics control), same `dev.iris.android.demo.bench` id, same
+      `CN=ai-app` signing cert, copied to `~/host/bench/
+      iris-bench-arm64.apk` and `~/repos/ai-app-bench/iris/build/outputs/
+      apk/release/iris-bench-arm64.apk`; that repo's own README gained a
+      dated entry. Still not confirmed on Iris's actual phone.
+
+      **Redelivered again, 2026-09-06, a later pass.** Iris's report on
+      build a9232ac, with screenshots: text now the right size but
+      **blurry**; opening the keyboard still **wipes every glyph**
+      (rects stay, only text disappears); the **header buttons have
+      nothing behind them and overlap the transcript text**.
+
+      **1. The keyboard wipe.** Hypothesis (given in the task, confirmed
+      by reading the path before changing anything, per AGENTS.md):
+      `android::view::IrisViewPeer::surface_changed` fires on *every*
+      `SurfaceView` size/format change, not only a genuinely new
+      `Surface` -- showing the IME under `adjustResize` resizes the same
+      surface through this exact callback. The handler unconditionally
+      set `renderer = None` and called `AndroidRenderer::new`, which
+      builds a fresh, empty glyph atlas and fresh GPU buffers via
+      `UiRenderNode::new`, while `iris_core`'s CPU-side glyph cache
+      (`primitive/text.rs`) kept the atlas UV coordinates it had already
+      handed out against the *old* atlas -- every glyph then drew from a
+      rectangle pointing into a texture that had just been recreated
+      empty. Confirmed by reading `AndroidRenderer::resize` (already
+      existed, already did none of that -- only `surface.configure` and
+      the window uniform) against what `surface_changed` was actually
+      calling instead. **Fix**: `surface_changed` now calls
+      `AndroidRenderer::resize` when a renderer is already live, and only
+      builds a new one when `surface_changed` finds `renderer` still
+      `None` (a genuinely new surface -- after `surface_destroyed`, e.g.
+      backgrounding). Not independently re-verified against a forced IME
+      resize on this pass's emulator (no display keyboard exercised
+      end-to-end here); the reasoning is a direct code read plus the
+      existing `resize` path already being surface-only, not a
+      screenshot diff -- **the next agent with emulator time should do
+      the before/after screenshot this box originally asked for.**
+
+      **2. The blur.** Root cause: the P0 fix that made text the right
+      *size* (dividing the whole window into a "logical" space, then
+      letting the shader's NDC mapping stretch it back onto the real
+      framebuffer) rasterised each glyph at the small, pre-stretch size
+      and then displayed it stretched onto more physical pixels than it
+      had texels for. **Fix, and the density-independent length unit
+      Iris asked for the same day (IRIS_TODO.md) turned out to be the
+      same fix**: `Len::dp`, resolved against a `density` now carried on
+      `UiRenderState`/`Painter`, replaces the global stretch -- window
+      size, touch and insets are physical pixels throughout again
+      (`WindowInsets`, renamed from `LogicalInsets`), and
+      `TextBuffer::shape` multiplies `font_size`/`line_height` by density
+      before handing them to parley, so the atlas rasterises at the
+      display's real physical resolution. Full design in docs/LAYOUT.md's
+      "Density: `Len::dp`" section and the public-API summary in
+      docs/IRIS.md's 2026-09-06 entry.
+
+      **3. The header.** Only each button's own `rect(...)` painted
+      anything, so the gaps between/around them and the status-bar strip
+      above showed `CLEAR_COLOR` (black) one layer back, and the row's
+      reserved height was three `abs` (now-physical-pixel) button boxes
+      -- smaller than the dp-correct size the transcript below uses,
+      which is what read as "overlap" once the two disagreed. Fixed with
+      a `HEADER_SURFACE` rect stacked behind the whole row and every
+      header size moved onto `dp(...)`.
+
+      **4. Keyboard diagnostics, so Iris can report back even if a
+      keyboard-triggered regression persists.** `on_insets_changed` now
+      edge-triggers ~500ms after `ime_bottom` becomes non-zero, capturing
+      the same report the on-screen Diagnostics button produces, logging
+      it, copying it to the clipboard unprompted, and showing it in a new
+      plain-view overlay (`IrisView.showDiagnosticsOverlay`, Copy/Close)
+      that draws independently of iris's own renderer.
+
+      **Verified this pass**: `cargo fmt --all`, `cargo clippy --workspace
+      --all-targets` and `cargo clippy` on `android-app` (both `-D
+      warnings`, zero beyond the pre-existing `tabs-ui` unused-dependency
+      and wgpu future-incompat notices), `cargo test --workspace` (all
+      passing), `cargo ndk -t arm64-v8a check`/`clippy` for both the
+      `transcript-screen bench` feature set.
+
+      **Then run on this checkout's own emulator** (x86_64 debug,
+      `--features "transcript-screen force-gles bench"` -- this AVD has no
+      Vulkan adapter under a plain `-gpu host` boot, matching every prior
+      emulator finding in this file): `run-bench.sh` end to end, no crash,
+      `frames=534 janky%=79.03 ... cpu_p50=1.3ms`, 24/24 swipes, 400/400
+      streamed events -- unchanged in shape from prior readings, so the
+      diff cost nothing on the success path. **Header background**:
+      screenshot confirms the `HEADER_SURFACE` panel now sits behind all
+      three buttons (`/tmp/bench-after-run.png` this pass). **Keyboard
+      wipe**: forced a real `surface_changed` two ways -- `adb shell wm
+      size 1080x1900` (screenshot before/after, text intact) and actually
+      opening the soft keyboard via `settings put secure
+      show_ime_with_hard_keyboard 1` + tapping the message field
+      (ui-trace confirmed a real resize, elements moved -547px; keyboard
+      visible in the screenshot, text still fully rendered, not wiped).
+      Both are real evidence the reuse-renderer fix works, though neither
+      is the literal before/after diff this box originally asked for --
+      **still worth a deliberate side-by-side screenshot pair in a future
+      pass.**
+
+      **Found during this same verification, not fixed, needs a follow-up
+      pass**: after the keyboard-triggered resize, the top button row
+      appeared to render a **second time**, well below its real position,
+      inside the transcript's scroll area (same colours/text, unmistakably
+      the same three buttons) -- and a tap aimed at the composer's
+      "Message" field landed on "Run benchmark" instead (a second
+      benchmark run started, visible in logcat as two `iris bench report:`
+      lines from one session). Only seen after a resize with the keyboard
+      genuinely open; the plain `wm size` resize screenshot pair did not
+      show it, nor did the fresh-install screenshot before either resize.
+      **Not root-caused this pass** -- time ran out before isolating
+      whether this is the `Span::DOWN` two-phase draw (LAYOUT.md's
+      provisional-then-real placement) leaving a phase-1 primitive
+      retained somewhere it should have been moved from, something
+      specific to the keyboard's `on_insets_changed` rebuild racing a
+      redraw, or unrelated to this pass's changes entirely (not verified
+      against a build predating this session's commits, so do not treat
+      "caused by this pass" as established -- MACHINE.md's pinned rule
+      about not attributing without measuring applies here too). Also
+      noteworthy: `capture_keyboard_diagnostics` never fired in this
+      session (no "iris keyboard diagnostics" log line) despite the
+      keyboard visibly opening -- `on_insets_changed`'s `ime_bottom` may
+      not be populated the way expected on this emulator/API level, or
+      the duplicate-row state above interfered; **also needs a follow-up
+      pass** before relying on the auto-capture on a real phone.
+
+      **Not verified this pass**: anything on Iris's real phone, the
+      two-density crispness check IRIS_TODO.md's unit item asks for, and
+      the two open items just above.
+
+      **Fling and jitter, 2026-09-06.** The two `IRIS_TODO.md` "From the
+      phone" items this box's own text names as follow-ups are fixed --
+      `List::fling`/`VelocityTracker`/`FlingCalculator` (IRIS.md's
+      2026-09-06 entry) and the `DragArbiter` slop-release jump (fixed by
+      applying only the excess past `DRAG_SLOP` on the crossing frame,
+      not the whole pre-threshold drag) -- both wired through
+      `Selection::drag`'s release path, both covered by new unit tests in
+      `iris/src/sense.rs` and `iris/src/widget/list.rs`. **Root-caused by
+      reading `DragArbiter::update` and testing it directly, not by an
+      emulator trace** -- this pass did not open an emulator, so the
+      "trace the list's offset per frame" verification this box's own
+      todo asked for is still open, as is a feel-check of the fling on
+      real touch input. **Benchmark v2's four-phase spec (fling/stream/
+      type/keyboard) in `bench_client.rs` was not attempted this pass** --
+      wiring a real IME show/hide and refresh-rate read through
+      `bench_jni.rs`, and `FrameReport`'s per-phase accounting, is real
+      scope on its own and was left rather than shipped half-verified;
+      the Compose half above is already done and is the reference shape
+      for whoever picks this up. No redelivery this pass.
+
 - [ ] **P1 — session screen parity.** History paging backward (with the
       page-boundary healing `client-core` does not have yet, below),
       `TranscriptSource`-backed cache/server stitching, jump-to-latest,

docs/bench/compose-phone-2026-09-06.md

@@ -0,0 +1,73 @@
+# Compose bench report from Iris's phone, 2026-09-06
+
+The Compose half of P0 (RUST.md), run by Iris on her own phone and pasted
+back verbatim. The iris half's report goes beside it in this directory
+when it exists. Her caveat, worth keeping with the numbers: "I don't think
+this is entirely fair because the UI for iris is more minimal" -- the
+Compose screen also draws the usage bar, the status row and tool cards,
+which the iris bench screen does not yet. Her impression of the iris build
+before its first-touch bug: "it already feels very smooth so far".
+
+What to read first: the phone runs at 120 Hz, so the budget is 8.3 ms;
+`late` is measured against that. Compose's tail is the streaming phase --
+`markdown reparsed while streaming: 396, 8.5ms mean, 25.8ms worst` and
+`record: one block: 398, 6.3ms mean, 19.9ms worst` -- which is exactly the
+path iris's `TranscriptScreen::apply` (replace the last row only) is meant
+to beat. Process CPU over the run is 20.9 s of a 38.5 s run; peak RSS
+587 MB; battery current mean 419 mA.
+
+```
+ai-app render report
+device: Pixel 9 Pro XL (Google), Android 17
+build: release
+
+transcript:
+  43 events, 41 rows, 93 units loaded
+  viewport 1333px, 2 units visible
+  on screen: the list's own 0px, AssistantMsg 24520px
+  0 tool calls and 0 groups open
+
+frames:
+  1613 frames over 38.5s at 120Hz (8.3ms budget)
+  late: 742 (46.0%)
+  total  p50 7.7ms  p90 29.2ms  p99 41.1ms
+  waited p50 0.5ms  p90 12.9ms  p99 27.2ms
+  input  p50 0.0ms  p90 0.0ms  p99 0.0ms
+  anim   p50 1.1ms  p90 5.8ms  p99 9.5ms
+  layout p50 0.0ms  p90 0.1ms  p99 0.2ms
+  draw   p50 0.4ms  p90 15.9ms  p99 27.9ms
+  sync   p50 0.1ms  p90 0.5ms  p99 1.0ms
+  issue  p50 1.1ms  p90 1.7ms  p99 3.0ms
+  swap   p50 0.4ms  p90 0.5ms  p99 0.7ms
+  gpu    p50 1.8ms  p90 2.1ms  p99 6.6ms
+
+where the draw phase went:
+  draw phase 3.83ms per frame, of which:
+    the transcript: 0.25ms (measure 0.15, place 0.10, record 0.00)
+    everything else: 3.58ms (93%)
+
+work since this was last copied:
+  draw: the whole transcript: 12, 0.2ms total, 0.0ms mean, 0.0ms worst
+  grouped tool runs: 398, 10.3ms total, 0.0ms mean, 0.1ms worst
+  markdown cut into pieces: 1, 0.0ms total, 0.0ms mean, 0.0ms worst
+  markdown parsed while composing: 7, 3.0ms total, 0.4ms mean, 0.5ms worst
+  markdown ready: 46
+  markdown reparsed while streaming: 396, 3384.6ms total, 8.5ms mean, 25.8ms worst
+  markdown warmed: 1, 1.4ms total, 1.4ms mean, 1.4ms worst
+  measure: the whole transcript: 957, 248.7ms total, 0.3ms mean, 15.7ms worst
+  message composed: 403
+  message cut into parts: 1, 0.1ms total, 0.1ms mean, 0.1ms worst
+  place: the whole transcript: 1319, 162.4ms total, 0.1ms mean, 1.3ms worst
+  record: one block: 398, 2498.7ms total, 6.3ms mean, 19.9ms worst
+  session screen recomposed: 413
+  status row recomposed: 1
+  unit composed: 538
+  units flattened: 399, 44.3ms total, 0.1ms mean, 0.5ms worst
+  usage bar recomposed: 413
+
+bench:
+  scroll: 6 cycles (24 swipes), streamed 400/400 fixture events
+  process CPU time over this run: 20907ms
+  peak RSS: 587356kB
+  battery current: mean -418509µA over 39 samples (min -1988281, max -107812)
+```

docs/bench/compose-phone-v2-2026-09-06.md

@@ -0,0 +1,93 @@
+# Compose bench v2 report from Iris's phone, 2026-09-06
+
+Bench v2 (fling / stream / type / keyboard, RUST.md's P0 box) on the
+Compose `bench` build, run by Iris on her Pixel 9 Pro XL, verbatim. Note
+the display was at **60 Hz** for this run (16.7 ms budget) where the v1
+run was at 120 Hz -- the phone's adaptive refresh rate decides, and
+`late` is judged against whichever it was, so compare a run with a run at
+the same rate. The iris v2 report goes beside this when it exists.
+
+What it says: fling, type and keyboard are all essentially clean on
+Compose (0.1%, 0.9% and 0% late; fling p50 5.5 ms, p99 11.6 ms). The
+whole tail is the streaming phase again -- 41.9% late, p99 42.5 ms,
+driven by `markdown reparsed while streaming` (8.6 ms mean, 30.3 ms
+worst) and `record: one block` (6.3 ms mean, 25.5 ms worst). Process CPU
+69.6 s over the 125.5 s run; peak RSS 577 MB; battery current mean
+571 mA over 126 samples.
+
+```
+ai-app render report
+device: Pixel 9 Pro XL (Google), Android 17
+build: release
+
+transcript:
+  108 events, 26 rows, 58 units loaded
+  viewport 1531px, 2 units visible
+  on screen: the list's own 0px, AssistantMsg 24520px
+  0 tool calls and 0 groups open
+
+per phase:
+  fling: 3278 frames over 32.7s
+    late: 4 (0.1%)
+      total  p50 5.5ms  p90 8.7ms  p99 11.6ms
+    worst 49.0ms
+  stream: 1041 frames over 21.3s
+    late: 436 (41.9%)
+      total  p50 13.4ms  p90 31.7ms  p99 42.5ms
+    worst 52.5ms
+  type: 2446 frames over 61.5s
+    late: 23 (0.9%)
+      total  p50 7.3ms  p90 13.2ms  p99 16.5ms
+    worst 38.9ms
+  keyboard: 358 frames over 10.0s
+    late: 0 (0.0%)
+      total  p50 6.3ms  p90 8.6ms  p99 11.1ms
+    worst 12.0ms
+
+frames:
+  7122 frames over 125.5s at 60Hz (16.7ms budget)
+  late: 463 (6.5%)
+  total  p50 6.0ms  p90 13.8ms  p99 34.0ms
+  waited p50 0.5ms  p90 1.1ms  p99 19.9ms
+  input  p50 0.0ms  p90 0.0ms  p99 0.0ms
+  anim   p50 0.7ms  p90 4.5ms  p99 7.6ms
+  layout p50 0.1ms  p90 0.1ms  p99 0.2ms
+  draw   p50 0.7ms  p90 2.9ms  p99 21.9ms
+  sync   p50 0.1ms  p90 0.2ms  p99 0.6ms
+  issue  p50 1.4ms  p90 2.4ms  p99 3.2ms
+  swap   p50 0.4ms  p90 0.8ms  p99 1.2ms
+  gpu    p50 1.5ms  p90 2.1ms  p99 6.6ms
+
+where the draw phase went:
+  draw phase 1.74ms per frame, of which:
+    the transcript: 0.24ms (measure 0.10, place 0.14, record 0.00)
+    everything else: 1.51ms (86%)
+
+work since this was last copied:
+  draw: the whole transcript: 280, 1.9ms total, 0.0ms mean, 0.0ms worst
+  grouped tool runs: 407, 18.6ms total, 0.0ms mean, 0.2ms worst
+  markdown cut into pieces: 40, 0.4ms total, 0.0ms mean, 0.0ms worst
+  markdown parsed while composing: 2, 1.6ms total, 0.8ms mean, 1.1ms worst
+  markdown ready: 323
+  markdown reparsed while streaming: 395, 3406.9ms total, 8.6ms mean, 30.3ms worst
+  markdown warmed: 40, 38.2ms total, 1.0ms mean, 4.3ms worst
+  measure: the whole transcript: 1978, 683.9ms total, 0.3ms mean, 15.9ms worst
+  message composed: 397
+  message cut into parts: 40, 2.9ms total, 0.1ms mean, 0.2ms worst
+  place: the whole transcript: 4308, 996.0ms total, 0.2ms mean, 2.4ms worst
+  record: one block: 394, 2472.7ms total, 6.3ms mean, 25.5ms worst
+  session screen recomposed: 1630
+  status row recomposed: 1
+  transcript page from server: 10
+  unit composed: 927
+  units flattened: 408, 85.5ms total, 0.2ms mean, 1.8ms worst
+
+bench:
+  fling: 8 flings out + 8 back at 12000px/s, travel start=idx=0/off=0px outward=idx=188/off=182px end=idx=0/off=0px
+  scroll: 6 cycles (24 swipes, legacy tween), streamed 400/400 fixture events
+  type: 600 characters inserted then deleted, one per 50ms
+  keyboard: shown 5/5, hidden 5/5 (confirmed via isImeVisible)
+  process CPU time over this run: 69564ms
+  peak RSS: 577452kB
+  battery current: mean -571483µA over 126 samples (min -2361718, max -99218)
+```

docs/bench/iris-phone-2026-09-06-before-fixes.md

@@ -0,0 +1,31 @@
+# iris bench report from Iris's phone, 2026-09-06, before the phone fixes
+
+Build 46246ea (Vulkan, bench v1: 24-swipe scroll loop then 400 streamed
+events), run by Iris on her Pixel 9 Pro XL before the first-touch wipe,
+the missing bold faces, the density scale and the status-bar inset were
+fixed -- so the rows were drawn at roughly a third of their intended size
+and the run may have included frames after the wipe. Preliminary, kept
+because it is the first iris number from real hardware. Compare with
+`compose-phone-2026-09-06.md`, taken on the same phone with the same
+fixture and gesture loop.
+
+Reading it: the phone is 120 Hz (8.3 ms budget). `janky%` here counts
+frames over 16.7 ms, so it is not Compose's `late` (over 8.3 ms). Like for
+like: iris p50 6.2 ms vs Compose 7.7 ms; p90 32.0 vs 29.2; p99 42.1 vs
+41.1. `cpu_p50=4.7ms` is iris's own per-frame CPU work on the phone,
+against 0.2-0.4 ms on the emulator's x86 cores. Process CPU 15.6 s vs
+20.9 s, but over a shorter run (692 frames vs 1613 -- iris only renders on
+change and had no fling settle time), so per-second CPU is not directly
+comparable; peak RSS 365 MB vs 587 MB. Battery current mean 563 mA vs
+419 mA is the one figure that reads worse, and it is the least
+comparable: 22 samples vs 39, over runs of different length and different
+idle share. Bench v2's per-phase accounting is what makes these comparable.
+
+```
+iris bench report
+frames=692 janky%=32.37 p50=6.2ms p90=32.0ms p99=42.1ms worst=52.6ms (measures redraw-start to after present() is called, not GPU/compositor completion) cpu_p50=4.7ms gpu_wait_p50=1.3ms (redraw-start-to-submit vs. submit-to-after-present)
+  scroll: 6 cycles (24 swipes), streamed 400/400 fixture events
+  process CPU time over this run: 15554ms
+  peak RSS: 365328kB
+  battery current: mean -563493µA over 22 samples (min -1807812, max -132812)
+```

event-model/src/lib.rs

@@ -305,6 +305,25 @@ pub enum Event {
     /// it, which is why this is written down rather than left to be inferred
     /// from a second example that does not exist.
     Cleared,
+    /// The account behind this session has no quota left, so the turn stopped
+    /// without finishing.
+    ///
+    /// Its own event rather than an [`Event::Error`] carrying the dialect's
+    /// sentence, because two things act on it that cannot read English: the
+    /// transcript draws it as a state the session is in rather than as a
+    /// failure of something it did, and `crate::resume` schedules the message
+    /// that picks the work back up. Recognising it belongs to the driver, which
+    /// is the only layer that knows its dialect's wording -- above here nothing
+    /// matches on strings.
+    ///
+    /// `resets_at` is epoch seconds, and `None` is a real state: the dialect
+    /// said the limit was hit without saying when it lifts. Nothing here
+    /// invents one -- what the wait is actually decided against is the usage
+    /// endpoint, and this is the hint that starts the waiting.
+    LimitReached {
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        resets_at: Option<f64>,
+    },
     Error {
         message: String,
     },

iris/Cargo.lock

@@ -1757,6 +1757,7 @@ dependencies = [
  "fxhash",
  "image",
  "parley",
+ "pollster",
  "swash",
  "wgpu",
 ]

iris/android-app/Cargo.lock

@@ -1785,6 +1785,7 @@ dependencies = [
  "fxhash",
  "image",
  "parley",
+ "pollster",
  "swash",
  "wgpu",
 ]

iris/android-app/app/src/main/java/dev/iris/android/demo/IrisView.java

@@ -1,6 +1,17 @@
 package dev.iris.android.demo;
 
+import android.app.Activity;
+import android.content.ClipData;
+import android.content.ClipboardManager;
 import android.content.Context;
+import android.view.Gravity;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.FrameLayout;
+import android.widget.LinearLayout;
+import android.widget.ScrollView;
+import android.widget.TextView;
 
 import org.linebender.android.rustview.RustView;
 
@@ -33,4 +44,112 @@ public final class IrisView extends RustView {
         unregisterInsetsNative(mViewPeer);
         super.onDetachedFromWindow();
     }
+
+    /**
+     * Called from the Rust side (iris/src/android/view.rs's
+     * `show_renderer_error`) when `AndroidRenderer::new` fails instead of
+     * drawing -- an ordinary instance method rather than a `native` one,
+     * since this call is Rust reaching into Java rather than the other
+     * direction. Replaces the whole activity content with plain,
+     * selectable, scrollable text rather than leaving the last frame (or a
+     * blank surface) on screen with no way to report what happened:
+     * UI_RULES.md's "a failure is reported where it happened, and says
+     * what to do next." No dialog and no styling beyond what is needed to
+     * read and copy the text -- this path exists for exactly the crash it
+     * replaces, so it must not depend on anything that could itself fail
+     * to render.
+     */
+    void showRendererError(String report) {
+        Context context = getContext();
+        if (!(context instanceof Activity)) {
+            return;
+        }
+        Activity activity = (Activity) context;
+        TextView text = new TextView(activity);
+        text.setText(report);
+        text.setTextIsSelectable(true);
+        text.setGravity(Gravity.TOP | Gravity.START);
+        int pad = (int) (16 * activity.getResources().getDisplayMetrics().density);
+        text.setPadding(pad, pad, pad, pad);
+        ScrollView scroll = new ScrollView(activity);
+        scroll.addView(text);
+        activity.setContentView(scroll);
+    }
+
+    private static final String DIAGNOSTICS_OVERLAY_TAG = "iris-diagnostics-overlay";
+
+    /**
+     * The bench build's keyboard diagnostics capture
+     * (`bench_client.rs`'s `on_insets_changed` /
+     * `capture_keyboard_diagnostics`, via `bench_jni.rs`'s
+     * `PlatformHandle::show_diagnostics_overlay`): unlike
+     * `showRendererError` above, this adds a panel *over* this view
+     * (`MainActivity`'s `FrameLayout` still holds `IrisView` underneath,
+     * running) rather than replacing the activity's content, and gives it
+     * a Copy button and a Close that removes the panel -- so it draws
+     * (and can be read) whether or not iris itself is still putting
+     * anything on screen, without abandoning the session that produced
+     * it. Runs on the UI thread regardless of which thread calls it,
+     * since the call comes from a background task (a delayed capture
+     * after the keyboard opens), and touching the view tree off the UI
+     * thread is undefined.
+     */
+    void showDiagnosticsOverlay(String report) {
+        Context context = getContext();
+        if (!(context instanceof Activity)) {
+            return;
+        }
+        Activity activity = (Activity) context;
+        activity.runOnUiThread(() -> {
+            ViewGroup parent = (ViewGroup) getParent();
+            if (parent == null) {
+                return;
+            }
+            View existing = parent.findViewWithTag(DIAGNOSTICS_OVERLAY_TAG);
+            if (existing != null) {
+                parent.removeView(existing);
+            }
+
+            float density = activity.getResources().getDisplayMetrics().density;
+            int pad = (int) (16 * density);
+
+            LinearLayout overlay = new LinearLayout(activity);
+            overlay.setTag(DIAGNOSTICS_OVERLAY_TAG);
+            overlay.setOrientation(LinearLayout.VERTICAL);
+            overlay.setBackgroundColor(0xEE000000);
+            overlay.setPadding(pad, pad, pad, pad);
+
+            TextView text = new TextView(activity);
+            text.setText(report);
+            text.setTextIsSelectable(true);
+            text.setTextColor(0xFFFFFFFF);
+            ScrollView scroll = new ScrollView(activity);
+            scroll.addView(text);
+            overlay.addView(scroll, new LinearLayout.LayoutParams(
+                    LinearLayout.LayoutParams.MATCH_PARENT, 0, 1f));
+
+            LinearLayout buttonRow = new LinearLayout(activity);
+            buttonRow.setOrientation(LinearLayout.HORIZONTAL);
+            buttonRow.setPadding(0, pad, 0, 0);
+
+            Button copy = new Button(activity);
+            copy.setText("Copy");
+            copy.setOnClickListener(v -> {
+                ClipboardManager clipboard =
+                        (ClipboardManager) activity.getSystemService(Context.CLIPBOARD_SERVICE);
+                if (clipboard != null) {
+                    clipboard.setPrimaryClip(ClipData.newPlainText("iris diagnostics", report));
+                }
+            });
+            Button close = new Button(activity);
+            close.setText("Close");
+            close.setOnClickListener(v -> parent.removeView(overlay));
+            buttonRow.addView(copy);
+            buttonRow.addView(close);
+            overlay.addView(buttonRow);
+
+            parent.addView(overlay, new FrameLayout.LayoutParams(
+                    FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT));
+        });
+    }
 }

iris/android-app/build-apk.sh

@@ -0,0 +1,90 @@
+#!/bin/sh
+# Builds iris-android-app end to end: the cdylib (cargo ndk, straight into
+# app/src/main/jniLibs/) then the APK (Gradle). Written to stop re-typing
+# the same incantation by hand every time (ANDROID_HOME/NDK exports, the
+# cargo ndk invocation, the keystore env for a release build, apksigner/
+# aapt2 verification) -- see docs/RUST.md's P0 box. Same shape as `app/
+# build-apk.sh` (the Compose app's own build script) and `app/
+# iris-scroll.sh` (no coordinates, set -eu, exit 0 on success).
+#
+# Usage: ./build-apk.sh [debug|release] [--abi arm64-v8a|x86_64] [--features "a b c"]
+#   debug/release default to debug (matches this-machine-android's "the
+#   emulator stays on debug" rule -- pass `release` explicitly for a phone
+#   build). --abi defaults to arm64-v8a (a phone/real device); pass
+#   x86_64 for this checkout's own AVD. --features defaults to
+#   "transcript-screen bench" -- deliberately *without* `force-gles`, unlike
+#   an earlier version of this default. `force-gles` (`iris/Cargo.toml`'s
+#   own doc) exists only to force the emulator off its default software
+#   Vulkan and onto GLES for one specific measurement (RUST.md's I5, "Where
+#   iris's frame time goes") -- it was never meant to reach a real device,
+#   but this script's old default put it in every arm64 build regardless,
+#   so the P0 bench APK delivered to Iris's phone forced GLES there too.
+#   That is the named hypothesis in RUST.md's P0 box ("iris bench crash on
+#   the phone, 2026-09-06"): a real Vulkan driver is what a phone should
+#   run, and GLES is the backend the same box's own SwiftShader finding
+#   already flagged as the fragile one for this shader's storage buffers.
+#   Pass `--features "transcript-screen force-gles bench"` explicitly for
+#   an emulator backend-isolation run; never for a build meant for a phone.
+set -eu
+cd "$(dirname "$0")"
+
+BUILD_TYPE="debug"
+ABI="arm64-v8a"
+FEATURES="transcript-screen bench"
+case "${1:-}" in
+    debug|release) BUILD_TYPE="$1"; shift ;;
+esac
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --abi) ABI="$2"; shift 2 ;;
+        --features) FEATURES="$2"; shift 2 ;;
+        *) echo "build-apk.sh: unknown argument: $1" >&2; exit 1 ;;
+    esac
+done
+
+SDK_ROOT="$HOME/Android/Sdk"
+export ANDROID_HOME="$SDK_ROOT"
+export ANDROID_SDK_ROOT="$SDK_ROOT"
+NDK_DIR=$(ls -d "$SDK_ROOT"/ndk/*/ 2>/dev/null | sort -V | tail -1)
+if [ -z "$NDK_DIR" ]; then
+    echo "build-apk.sh: no NDK found under $SDK_ROOT/ndk" >&2
+    exit 1
+fi
+export ANDROID_NDK_HOME="$NDK_DIR"
+
+echo "build-apk.sh: cargo ndk -t $ABI build ${BUILD_TYPE:+(${BUILD_TYPE})} --features \"$FEATURES\""
+if [ "$BUILD_TYPE" = "release" ]; then
+    cargo ndk -t "$ABI" -P 26 -o app/src/main/jniLibs/ build --release --features "$FEATURES"
+else
+    cargo ndk -t "$ABI" -P 26 -o app/src/main/jniLibs/ build --features "$FEATURES"
+fi
+
+GRADLE_TASK="assembleDebug"
+APK_DIR="app/build/outputs/apk/debug"
+APK_NAME="app-debug.apk"
+if [ "$BUILD_TYPE" = "release" ]; then
+    GRADLE_TASK="assembleRelease"
+    APK_DIR="app/build/outputs/apk/release"
+    APK_NAME="app-release.apk"
+    # Same key `app/build-apk.sh` (the Compose app) generates once under
+    # ~/.config/ai-app/release.jks -- see AGENTS.md's "Checking your work".
+    export AI_APP_KEYSTORE="$HOME/.config/ai-app/release.jks"
+    if [ ! -f "$AI_APP_KEYSTORE" ]; then
+        echo "build-apk.sh: no release key at $AI_APP_KEYSTORE -- run app/build-apk.sh once first" >&2
+        exit 1
+    fi
+    export AI_APP_KEYSTORE_PASSWORD
+    AI_APP_KEYSTORE_PASSWORD=$(cat "$AI_APP_KEYSTORE.password")
+fi
+
+gradle ":app:$GRADLE_TASK" --console=plain
+
+APK_PATH="$(pwd)/$APK_DIR/$APK_NAME"
+BUILD_TOOLS=$(ls -d "$SDK_ROOT"/build-tools/*/ | sort -V | tail -1)
+echo "--- aapt2 dump badging ---"
+"${BUILD_TOOLS}aapt2" dump badging "$APK_PATH" | head -5
+if [ "$BUILD_TYPE" = "release" ]; then
+    echo "--- apksigner verify ---"
+    "${BUILD_TOOLS}apksigner" verify --print-certs "$APK_PATH"
+fi
+echo "$APK_PATH"

iris/android-app/run-bench.sh

@@ -0,0 +1,64 @@
+#!/bin/sh
+# Installs and runs the iris `bench` build on this checkout's own emulator
+# (per this-machine-android's per-checkout-AVD rule; `emu serial` picks it)
+# and prints the report -- the iris half of `app/transcript-bench.sh`'s
+# job. No coordinates: the button is found by its accessibility label
+# through `ui-trace`, per AGENTS.md's "Driving the UI".
+#
+# Usage: ./run-bench.sh [--apk PATH]
+#   Defaults to this checkout's own release APK
+#   (app/build/outputs/apk/release/app-release.apk) if it exists, else the
+#   debug one -- build one first with ./build-apk.sh.
+set -eu
+cd "$(dirname "$0")"
+
+APK=""
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --apk) APK="$2"; shift 2 ;;
+        *) echo "run-bench.sh: unknown argument: $1" >&2; exit 1 ;;
+    esac
+done
+if [ -z "$APK" ]; then
+    if [ -f app/build/outputs/apk/release/app-release.apk ]; then
+        APK=app/build/outputs/apk/release/app-release.apk
+    else
+        APK=app/build/outputs/apk/debug/app-debug.apk
+    fi
+fi
+if [ ! -f "$APK" ]; then
+    echo "run-bench.sh: no APK at $APK -- run ./build-apk.sh first" >&2
+    exit 1
+fi
+
+SERIAL=$(emu serial)
+PKG=$(aapt2 dump badging "$APK" 2>/dev/null | sed -n "s/^package: name='\\([^']*\\)'.*/\\1/p")
+if [ -z "$PKG" ]; then
+    BUILD_TOOLS=$(ls -d "$HOME"/Android/Sdk/build-tools/*/ | sort -V | tail -1)
+    PKG=$("${BUILD_TOOLS}aapt2" dump badging "$APK" | sed -n "s/^package: name='\\([^']*\\)'.*/\\1/p")
+fi
+
+echo "run-bench.sh: installing $APK ($PKG) on $SERIAL"
+adb -s "$SERIAL" install -r "$APK" >/dev/null
+adb -s "$SERIAL" shell am force-stop "$PKG"
+adb -s "$SERIAL" logcat -c
+adb -s "$SERIAL" shell am start -n "$PKG/dev.iris.android.demo.MainActivity" >/dev/null
+
+ui-trace record -s "$SERIAL" -d 3000 --do "tap 'Run benchmark'" -o /tmp/run-bench-tap.txt >/dev/null
+
+# Poll for the report line rather than a fixed sleep -- the run itself is a
+# fixed script (24 swipes + a 20s streaming phase) but device speed varies.
+i=0
+while [ "$i" -lt 90 ]; do
+    LINE=$(adb -s "$SERIAL" logcat -d -s iris-android-app:I 2>/dev/null | grep "iris bench report:" || true)
+    if [ -n "$LINE" ]; then
+        break
+    fi
+    i=$((i + 1))
+    sleep 1
+done
+if [ -z "$LINE" ]; then
+    echo "run-bench.sh: no report after 90s -- check logcat by hand" >&2
+    exit 1
+fi
+adb -s "$SERIAL" logcat -d -s iris-android-app:I | grep -A 6 "iris bench report:"

iris/android-app/src/bench_client.rs

@@ -4,17 +4,21 @@
 //! `transcript-ui`'s real screen with no server -- a frame-time comparison
 //! that measures the renderer rather than the data or the network.
 //!
-//! **Reuses `transcript_client.rs`'s shape** (folded items, a full
+//! **Reuses `transcript_client.rs`'s shape** (folded items, the same
-//! `transcript_ui::build_tree` rebuild per event) with the network half
+//! `TranscriptScreen::apply` incremental update on every event) with the
-//! replaced by the checked-in fixture, embedded with `include_str!` --
+//! network half replaced by the checked-in fixture, embedded with
-//! `app/bench-fixture/assets/transcript.jsonl`, 1,915,760 bytes, generated
+//! `include_str!` -- `app/bench-fixture/assets/transcript.jsonl`,
-//! by `app/bench-fixture/generate.py` and never a real transcript (that
+//! 1,915,760 bytes, generated by `app/bench-fixture/generate.py` and never
-//! file's own README). The first 3,200 lines are the opening backlog,
+//! a real transcript (that file's own README). The first 3,200 lines are
-//! folded once through `client_core::transcript_fold::fold_page` exactly
+//! the opening backlog, folded once through
-//! as a real `/transcript` page would be; the remaining ~400 are the
+//! `client_core::transcript_fold::fold_page` exactly as a real
-//! streaming tail, replayed one at a time through `fold_event` -- the same
+//! `/transcript` page would be (then a full `transcript_ui::build_tree`,
-//! fold path a live SSE reply arrives on -- by the "Run benchmark"
+//! same as any first load); the remaining ~400 are the streaming tail,
-//! control below.
+//! replayed one at a time through `fold_event` -- the same fold path a
+//! live SSE reply arrives on -- by the "Run benchmark" control below.
+//! Streaming through `apply` rather than a full rebuild per event is what
+//! this file exists to measure -- see docs/RUST.md's P0 box for the
+//! before/after report.
 
 use crate::bench_jni::PlatformHandle;
 use android_view::jni::{JavaVM, objects::GlobalRef};
@@ -54,6 +58,12 @@ pub struct BenchClient {
     ui_state: AndroidUiState,
     content: WeakWidget<WidgetPtr>,
     report_display: WeakWidget<TextEdit>,
+    /// The top button row, in a `WidgetPtr` slot rather than added
+    /// directly (like `content`) so `on_insets_changed` can swap in a
+    /// version padded for the status bar once insets are known -- RUST.md's
+    /// P0 box, "the status-bar inset is not applied," found the row sitting
+    /// directly under it because nothing here read `insets().top` at all.
+    top_bar: WeakWidget<WidgetPtr>,
     screen: Option<transcript_ui::TranscriptScreen>,
     items: Vec<TranscriptItem>,
     /// The events not yet streamed -- consumed by `start_benchmark`'s own
@@ -64,6 +74,13 @@ pub struct BenchClient {
     platform: Option<Arc<PlatformHandle>>,
     last_report: Option<String>,
     running: bool,
+    /// Edge-triggers the keyboard diagnostics capture below -- set on the
+    /// first `on_insets_changed` where `ime_bottom > 0.0`, cleared on the
+    /// first where it is not, so opening the keyboard fires this once
+    /// rather than on every insets update while it stays open (a rotation
+    /// or a status-bar change with the keyboard already up would otherwise
+    /// re-fire it).
+    keyboard_was_visible: bool,
 }
 
 impl HasAndroidUiState for BenchClient {
@@ -168,27 +185,48 @@ impl AndroidAppState for BenchClient {
             .label("Benchmark report")
             .add(rsc);
 
-        let controls = bench_controls(rsc);
+        let top_bar = WidgetPtr::new().add(rsc);
+        let controls = bench_controls(rsc, 0.0);
+        top_bar(rsc).set(controls);
         let tree = (
-            controls,
+            top_bar,
             content.height(rest(2)),
-            report_display.height(rest(1)).pad(8),
+            report_display.height(rest(1)).pad(dp(8)),
         )
             .span(Dir::DOWN)
             .add_strong(rsc)
             .any();
         ui_state.set_root(tree);
 
+        // Startup log line (RUST.md's P0 box, "log once at startup ... the
+        // number of font families found, the default family resolved"):
+        // what font discovery actually found on this device, before
+        // anything is drawn.
+        let font = rsc.ui.text.font_diagnostics();
+        log::info!(
+            "iris fonts: {} families found, default={:?} mono={:?}, resolved regular={:?} \
+             bold={:?} italic={:?} mono={:?}",
+            font.families_found,
+            font.default_family,
+            font.default_mono_family,
+            font.regular_resolved,
+            font.bold_resolved,
+            font.italic_resolved,
+            font.mono_resolved,
+        );
+
         let mut client = Self {
             ui_state,
             content,
             report_display,
+            top_bar,
             screen: None,
             items: Vec::new(),
             stream_tail: Vec::new(),
             platform: None,
             last_report: None,
             running: false,
+            keyboard_was_visible: false,
         };
 
         let (backlog, stream_tail) = parse_fixture();
@@ -212,11 +250,84 @@ impl AndroidAppState for BenchClient {
     fn back_pressed(&mut self, _rsc: &mut AndroidRsc<Self>, _render: &mut UiRenderState) -> bool {
         false
     }
+
+    /// Pads the top button row by the status-bar inset -- see `top_bar`'s
+    /// field comment. Rebuilds the row rather than mutating a stored
+    /// `Padding` in place, since nothing here holds a handle to one.
+    ///
+    /// **Also the trigger for the keyboard diagnostics capture** (RUST.md's
+    /// P0 box): the IME resizing the surface is exactly the case the
+    /// previous commit found wiped text, and Iris needs a way to get a
+    /// report off the phone even if that (or some other keyboard-triggered
+    /// regression) is still happening on the build she is holding --
+    /// `capture_keyboard_diagnostics` below fires ~500ms after the
+    /// keyboard becomes visible, once per keyboard opening, and shows its
+    /// report in a plain overlay view that draws independently of
+    /// whatever iris itself is doing.
+    fn on_insets_changed(
+        &mut self,
+        rsc: &mut AndroidRsc<Self>,
+        insets: iris::android::WindowInsets,
+    ) {
+        let controls = bench_controls(rsc, insets.top);
+        (self.top_bar)(rsc).set(controls);
+
+        let ime_visible = insets.ime_bottom > 0.0;
+        if ime_visible && !self.keyboard_was_visible {
+            self.keyboard_was_visible = true;
+            let redraw = rsc.tasks.redraw_handle();
+            rsc.spawn_task(async move |mut ctx| {
+                tokio::time::sleep(Duration::from_millis(KEYBOARD_DIAGNOSTICS_DELAY_MS)).await;
+                ctx.update(|state: &mut BenchClient, rsc| {
+                    state.capture_keyboard_diagnostics(rsc);
+                });
+                redraw.request_redraw();
+            });
+        } else if !ime_visible {
+            self.keyboard_was_visible = false;
+        }
+    }
 }
 
+/// How long to wait after the keyboard becomes visible before capturing
+/// diagnostics -- long enough that the resize, the reported wipe (if it is
+/// still happening) and a couple of frames have all had time to land, per
+/// AGENTS.md's "so that operations that finish in milliseconds have states
+/// on the way that nothing can observe" reasoning applied the other way:
+/// this wants to observe the state *after* the transition settles, not
+/// mid-flight.
+const KEYBOARD_DIAGNOSTICS_DELAY_MS: u64 = 500;
+
 type Rsc = AndroidRsc<BenchClient>;
 
-fn bench_controls(rsc: &mut Rsc) -> WeakWidget {
+/// The header row's own backdrop -- see `bench_controls`'s doc comment on
+/// why it needs one at all. A dark neutral rather than pure black
+/// (`android::render::CLEAR_COLOR`) so the row reads as a distinct panel
+/// instead of a hole in the background the buttons happen to float in.
+const HEADER_SURFACE: UiColor = UiColor::new(28, 28, 34, 255);
+
+/// `top_pad` is the status-bar inset in physical pixels (0.0 until
+/// `on_insets_changed` has run once) -- folded in here, rather than
+/// exposing the unadded builder for a caller to `.pad()` itself, because
+/// naming that builder's type at each call site is more machinery than a
+/// top-of-screen padding number is worth.
+///
+/// **Backed by an opaque rect the full size of the row, not just the three
+/// buttons.** Iris's phone report (docs/RUST.md's P0 box, screenshots on
+/// build a9232ac): "the header buttons have nothing behind them and
+/// overlap the transcript text" -- before this, only each button's own
+/// `rect(...)` painted anything, so the gaps between and around them (and
+/// the status-bar strip above them) showed whatever was one layer back
+/// (`CLEAR_COLOR`, black), and the row's true height was three
+/// physical-pixel-sized (`abs`, not `dp`) button boxes rather than the
+/// density-correct size the transcript below was already using post-P0 --
+/// exactly what reads as "overlap" once the two disagree. Fixed two ways
+/// together: a `HEADER_SURFACE` rect stacked behind the whole row (this
+/// function), and every size below moved from a bare number (physical
+/// pixels) to `dp(...)` (IRIS_TODO.md's density-independent length unit),
+/// so the row's reserved height in the outer `Span::DOWN`
+/// (`AndroidAppState::new`) matches what is actually painted.
+fn bench_controls(rsc: &mut Rsc, top_pad: f32) -> StrongWidget {
     let run_rect = rect(Color::rgb(40, 70, 40))
         .on(
             CursorSense::click(),
@@ -230,7 +341,7 @@ fn bench_controls(rsc: &mut Rsc) -> WeakWidget {
         wtext("Run benchmark").size(18).text_align(Align::CENTER),
     )
         .stack()
-        .pad(8)
+        .pad(dp(8))
         .add(rsc);
 
     let copy_rect = rect(Color::rgb(50, 50, 60))
@@ -246,10 +357,33 @@ fn bench_controls(rsc: &mut Rsc) -> WeakWidget {
         wtext("Copy report").size(18).text_align(Align::CENTER),
     )
         .stack()
-        .pad(8)
+        .pad(dp(8))
         .add(rsc);
 
-    (run, copy).span(Dir::RIGHT).height(56).add(rsc)
+    let diag_rect = rect(Color::rgb(60, 45, 70))
+        .on(
+            CursorSense::click(),
+            |ctx: EventIdCtx<'_, Rsc, _, _>, rsc: &mut Rsc| {
+                ctx.state.show_diagnostics(rsc);
+            },
+        )
+        .label("Diagnostics");
+    let diagnostics = (
+        diag_rect,
+        wtext("Diagnostics").size(18).text_align(Align::CENTER),
+    )
+        .stack()
+        .pad(dp(8))
+        .add(rsc);
+
+    let buttons = (run, copy, diagnostics).span(Dir::RIGHT).add(rsc);
+
+    (rect(HEADER_SURFACE), buttons)
+        .stack()
+        .height(dp(56))
+        .pad(Padding::top(top_pad))
+        .add_strong(rsc)
+        .any()
 }
 
 impl BenchClient {
@@ -266,6 +400,56 @@ impl BenchClient {
         self.screen = Some(screen);
     }
 
+    /// RUST.md's P0 box: "a named `Diagnostics` control ... with 'copy this
+    /// and send it to Iris'." Fills `report_display` (the same TextEdit the
+    /// benchmark report uses) rather than a separate widget, so the
+    /// existing "Copy report" button and clipboard path work on whichever
+    /// text is currently shown -- `last_report` is what `copy_report` reads,
+    /// so it's set here too rather than adding a second copy path.
+    fn show_diagnostics(&mut self, rsc: &mut Rsc) {
+        let font = rsc.ui.text.font_diagnostics();
+        let frame_report = match self.android_state().frame_report.report() {
+            Some(stats) => format!("{stats}"),
+            None => "no frames recorded yet".to_string(),
+        };
+        let report = match &self.android_state().renderer {
+            Some(renderer) => renderer.diagnostics_report(&font, &frame_report),
+            None => "iris diagnostics: no renderer yet (no surface)".to_string(),
+        };
+        self.report_display.edit(rsc).set(&report);
+        self.last_report = Some(report);
+    }
+
+    /// The keyboard's own diagnostics capture -- see `on_insets_changed`'s
+    /// doc comment. Reuses `show_diagnostics`'s exact report (so it is the
+    /// same text the on-screen `Diagnostics` button produces, plus the
+    /// per-frame log `FrameReport` already keeps around the resize --
+    /// `frame_report.report()` above covers "the frames around the
+    /// resize" without a second accounting mechanism), then does three
+    /// things the button does not: logs it (so a `logcat` pull gets it
+    /// even if nothing on screen does), copies it to the clipboard
+    /// unprompted, and shows it in the shell's plain overlay view, which
+    /// draws independently of iris's own renderer -- the whole point,
+    /// since the renderer is exactly what might be in the wiped state
+    /// this exists to report on.
+    fn capture_keyboard_diagnostics(&mut self, rsc: &mut Rsc) {
+        self.show_diagnostics(rsc);
+        let Some(report) = self.last_report.clone() else {
+            return;
+        };
+        log::info!("iris keyboard diagnostics:\n{report}");
+        let Some(platform) = &self.platform else {
+            log::info!("iris keyboard diagnostics: no platform handle, can't reach the shell");
+            return;
+        };
+        if platform.copy_to_clipboard("iris keyboard diagnostics", &report) {
+            log::info!("iris keyboard diagnostics: copied to clipboard");
+        } else {
+            log::info!("iris keyboard diagnostics: clipboard copy failed");
+        }
+        platform.show_diagnostics_overlay(&report);
+    }
+
     fn copy_report(&mut self) {
         let Some(report) = &self.last_report else {
             log::info!("iris bench report: nothing to copy -- run the benchmark first");
@@ -344,8 +528,15 @@ impl BenchClient {
             let mut sent = 0usize;
             for event in stream_tail.into_iter().take(total) {
                 ctx.update(move |state: &mut BenchClient, rsc| {
+                    let old_items = state.items.clone();
                     state.items = fold_event(&state.items, &event);
-                    state.rebuild_transcript(rsc);
+                    match &state.screen {
+                        // The path P0 asked to measure: update only the
+                        // row(s) that changed instead of rebuilding all
+                        // ~3,200 of them per event.
+                        Some(screen) => screen.apply(rsc, &old_items, &state.items),
+                        None => state.rebuild_transcript(rsc),
+                    }
                 });
                 redraw.request_redraw();
                 sent += 1;

iris/android-app/src/bench_jni.rs

@@ -131,4 +131,31 @@ impl PlatformHandle {
         .ok()?;
         Some(())
     }
+
+    /// Shows `report` in the shell's plain-view diagnostics overlay
+    /// (`IrisView.showDiagnosticsOverlay`) -- a real `TextView` plus Copy
+    /// and Close controls, added over whatever iris itself is drawing
+    /// rather than replacing it (unlike `android::view::show_renderer_error`,
+    /// which exists for the case the renderer can never recover from and
+    /// intentionally never returns). Called from a background task after
+    /// the keyboard-open delay (`bench_client.rs`'s `on_insets_changed`),
+    /// so the Java side hops onto the UI thread itself before touching the
+    /// view tree -- see that method's own comment.
+    pub fn show_diagnostics_overlay(&self, report: &str) -> bool {
+        self.try_show_diagnostics_overlay(report).is_some()
+    }
+
+    fn try_show_diagnostics_overlay(&self, report: &str) -> Option<()> {
+        let mut guard = self.vm.attach_current_thread().ok()?;
+        let env: &mut JNIEnv = &mut guard;
+        let jreport = env.new_string(report).ok()?;
+        env.call_method(
+            self.view.as_obj(),
+            "showDiagnosticsOverlay",
+            "(Ljava/lang/String;)V",
+            &[JValue::Object(jreport.as_ref())],
+        )
+        .ok()?;
+        Some(())
+    }
 }

iris/android-app/src/transcript_client.rs

@@ -20,14 +20,22 @@
 //! **Reuses `iris/desktop-app`'s `app.rs` shape almost exactly** --
 //! `fold_event`/`group_tool_runs`/`fold_page`/`raw_seq` from
 //! `client_core::transcript_fold`, a `generation` counter guarding against
-//! a stale background response, and a full rebuild of the widget tree on
+//! a stale background response. What differs is only the redraw
-//! every event (same tradeoff, same reason: `push_row` cannot update a row
+//! mechanism: android-view has no `winit::EventLoopProxy`, so this uses
-//! already on screen, and this rig's conversations are small). What
+//! `iris::task::Tasks::redraw_handle` (new, added alongside this box) to
-//! differs is only the redraw mechanism: android-view has no
+//! request a frame after each `TaskCtx::update` instead of relying on
-//! `winit::EventLoopProxy`, so this uses `iris::task::Tasks::redraw_handle`
+//! `Tasks::spawn`'s single end-of-future redraw -- see that method's own
-//! (new, added alongside this box) to request a frame after each
+//! doc for why.
-//! `TaskCtx::update` instead of relying on `Tasks::spawn`'s single
+//!
-//! end-of-future redraw -- see that method's own doc for why.
+//! **Streaming no longer costs a full rebuild** (fixed after the P0 gate
+//! showed why it mattered -- 20 events/second means 20 rebuilds/second of
+//! a ~3,200-row transcript otherwise): `apply_event` calls
+//! `transcript_ui::TranscriptScreen::apply` with the item list before and
+//! after `fold_event`, which updates only the row(s) that actually
+//! changed (almost always just the one open assistant message) instead of
+//! refolding and rebuilding every row. `rebuild_transcript` still runs
+//! the whole widget tree once, for the opening page and for `apply`'s own
+//! rare regroup fallback.
 
 use client_core::api::{ApiClient, UreqTransport};
 use client_core::event_stream::{StreamItem, follow_session_events};
@@ -360,8 +368,17 @@ impl TranscriptClient {
     }
 
     fn apply_event(&mut self, rsc: &mut AndroidRsc<Self>, event: &SeqEvent) {
+        let old_items = self.items.clone();
         self.items = fold_event(&self.items, event);
-        self.rebuild_transcript(rsc);
+        match &self.screen {
+            // The common path: update only the row(s) that actually
+            // changed instead of refolding and rebuilding all ~3,200 of
+            // them per event (RUST.md's P0 streaming-phase fix).
+            Some(screen) => screen.apply(rsc, &old_items, &self.items),
+            // No screen yet (the opening page hasn't landed) -- build one
+            // the ordinary way once it has.
+            None => self.rebuild_transcript(rsc),
+        }
     }
 
     fn send_message(&mut self, session_id: String, text: String) {

iris/core/Cargo.toml

@@ -5,6 +5,12 @@ edition.workspace = true
 
 [dependencies]
 wgpu = { workspace = true }
+# Only for `UiRenderNode::new`'s `push_error_scope`/`pop_error_scope` pair
+# (renderer-creation error reporting, RUST.md's P0 phone-crash box) --
+# `block_on` turns that one async pop into the same synchronous call shape
+# `device_limits()`'s two callers already use for `request_adapter`/
+# `request_device`, rather than making this crate's one entry point async.
+pollster = { workspace = true }
 bytemuck ={ workspace = true }
 image = { workspace = true }
 parley = { workspace = true }

iris/core/assets/fonts/OFL.txt

@@ -0,0 +1,201 @@
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iris/core/src/orientation/len.rs

@@ -9,7 +9,31 @@ pub struct Size {
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Len {
+    /// Physical pixels -- a raw device pixel, unaffected by the display's
+    /// density. Rare to want directly (a hairline border is the usual
+    /// case); most sizes should be `dp` instead. See `dp`'s own doc for why
+    /// the two are kept separate rather than one field a caller has to
+    /// remember to pre-multiply.
     pub abs: f32,
+    /// Density-independent pixels -- Android's `dp` / CSS's reference pixel
+    /// (1 unit = 1/160in), resolved against the display's density at
+    /// layout time (`apply_rest`'s `density` parameter) rather than at the
+    /// point a widget is built, since density is a property of the device
+    /// this ends up running on, not of the widget tree. This is the unit
+    /// IRIS_TODO.md's "a density-independent length unit" item asked for,
+    /// 2026-09-06: before it existed, every size in the tree was `abs`
+    /// (physical pixels), and the only way to make a 16px design draw at
+    /// the right *size* on a denser display was a single global multiply
+    /// applied to the whole rendered scene after layout -- which is also
+    /// what made text blurry (RUST.md's P0 box, "blurry ... glyphs drawn
+    /// at logical size and stretched by the scale"): a glyph rasterised at
+    /// 16 physical px and then stretched 3x by that global multiply is a
+    /// 48px area sampled from a 16px bitmap. Resolving `dp` per-length at
+    /// layout time instead means the font size handed to the text shaper
+    /// is already the physical size (`16.0.dp() * 3.0`), so the glyph
+    /// atlas rasterises at the display's real resolution and nothing
+    /// downstream needs to stretch anything.
+    pub dp: f32,
     pub rel: f32,
     pub rest: f32,
 }
@@ -67,10 +91,10 @@ impl Size {
         }
     }
 
-    pub fn to_uivec2(self) -> UiVec2 {
+    pub fn to_uivec2(self, density: f32) -> UiVec2 {
         UiVec2 {
-            x: self.x.apply_rest(),
+            x: self.x.apply_rest(density),
-            y: self.y.apply_rest(),
+            y: self.y.apply_rest(density),
         }
     }
 
@@ -98,26 +122,43 @@ impl Size {
 impl Len {
     pub const ZERO: Self = Self {
         abs: 0.0,
+        dp: 0.0,
         rel: 0.0,
         rest: 0.0,
     };
 
     pub const REST: Self = Self {
         abs: 0.0,
+        dp: 0.0,
         rel: 0.0,
         rest: 1.0,
     };
 
-    pub fn apply_rest(&self) -> UiScalar {
+    /// Resolves to a `UiScalar`, folding `dp` into `abs` pixels against
+    /// `density` (physical pixels per dp -- 1.0 on a desktop or an
+    /// unscaled display, `content_scale` on Android; see `dp`'s field
+    /// doc). Every other component of `Len` is already resolution-
+    /// independent (`rel` is a fraction of the parent; `rest` becomes a
+    /// fraction too, below), so `density` only ever touches this one term.
+    pub fn apply_rest(&self, density: f32) -> UiScalar {
         UiScalar {
             rel: self.rel + if self.rest > 0.0 { 1.0 } else { 0.0 },
-            abs: self.abs,
+            abs: self.abs + self.dp * density,
         }
     }
 
     pub fn abs(abs: impl UiNum) -> Self {
         Self {
             abs: abs.to_f32(),
+            dp: 0.0,
+            rel: 0.0,
+            rest: 0.0,
+        }
+    }
+    pub fn dp(dp: impl UiNum) -> Self {
+        Self {
+            abs: 0.0,
+            dp: dp.to_f32(),
             rel: 0.0,
             rest: 0.0,
         }
@@ -125,6 +166,7 @@ impl Len {
     pub fn rel(rel: impl UiNum) -> Self {
         Self {
             abs: 0.0,
+            dp: 0.0,
             rel: rel.to_f32(),
             rest: 0.0,
         }
@@ -132,6 +174,7 @@ impl Len {
     pub fn rest(ratio: impl UiNum) -> Self {
         Self {
             abs: 0.0,
+            dp: 0.0,
             rel: 0.0,
             rest: ratio.to_f32(),
         }
@@ -144,6 +187,15 @@ pub mod len_fns {
     pub fn abs(abs: impl UiNum) -> Len {
         Len {
             abs: abs.to_f32(),
+            dp: 0.0,
+            rel: 0.0,
+            rest: 0.0,
+        }
+    }
+    pub fn dp(dp: impl UiNum) -> Len {
+        Len {
+            abs: 0.0,
+            dp: dp.to_f32(),
             rel: 0.0,
             rest: 0.0,
         }
@@ -151,6 +203,7 @@ pub mod len_fns {
     pub fn rel(rel: impl UiNum) -> Len {
         Len {
             abs: 0.0,
+            dp: 0.0,
             rel: rel.to_f32(),
             rest: 0.0,
         }
@@ -158,14 +211,15 @@ pub mod len_fns {
     pub fn rest(ratio: impl UiNum) -> Len {
         Len {
             abs: 0.0,
+            dp: 0.0,
             rel: 0.0,
             rest: ratio.to_f32(),
         }
     }
 }
 
-impl_op!(Len Add add; abs rel rest);
+impl_op!(Len Add add; abs dp rel rest);
-impl_op!(Len Sub sub; abs rel rest);
+impl_op!(Len Sub sub; abs dp rel rest);
 
 impl_op!(Size Add add; x y);
 impl_op!(Size Sub sub; x y);
@@ -187,6 +241,9 @@ impl std::fmt::Display for Len {
         if self.abs != 0.0 {
             write!(f, "{} abs;", self.abs)?;
         }
+        if self.dp != 0.0 {
+            write!(f, "{} dp;", self.dp)?;
+        }
         if self.rel != 0.0 {
             write!(f, "{} rel;", self.rel)?;
         }

iris/core/src/primitive/text.rs

@@ -2,14 +2,63 @@ use crate::{Align, GlyphAtlas, GlyphKey, PlacedGlyph, RegionAlign, Textures, UiC
 use parley::{
     Alignment, AlignmentOptions, FontContext, FontFamily, FontFamilyName, FontStyle, FontWeight,
     GenericFamily, Layout, LayoutContext, LineHeight, PositionedLayoutItem, StyleProperty,
+    fontique::{Blob, FamilyId},
 };
 use std::ops::Range;
+use std::sync::Arc;
 use swash::{
     FontRef,
     scale::{Render, ScaleContext, Source, StrikeWith},
     zeno::{Format, Vector},
 };
 
+/// Bundled fonts, registered over the system collection rather than relied
+/// on alone -- see `TextData::register_bundled_fonts`'s doc comment for
+/// why. Static weight/style cuts, not a variable font: parley/fontique
+/// resolve a variable font's weight axis by picking normalized coordinates
+/// on whatever single face registers for the family, and a phone whose
+/// system "Roboto" is actually the variable "Roboto Flex" is exactly the
+/// device class this sidesteps, rather than depends on working correctly.
+/// Noto Sans, OFL-licensed (`assets/fonts/OFL.txt`), chosen for coverage
+/// breadth (a transcript's content is not known in advance) over a
+/// smaller-footprint alternative -- see the doc comment for the size this
+/// added.
+const NOTO_SANS_REGULAR: &[u8] = include_bytes!("../../assets/fonts/NotoSans-Regular.ttf");
+const NOTO_SANS_BOLD: &[u8] = include_bytes!("../../assets/fonts/NotoSans-Bold.ttf");
+const NOTO_SANS_ITALIC: &[u8] = include_bytes!("../../assets/fonts/NotoSans-Italic.ttf");
+const NOTO_SANS_BOLD_ITALIC: &[u8] = include_bytes!("../../assets/fonts/NotoSans-BoldItalic.ttf");
+const NOTO_SANS_MONO_REGULAR: &[u8] = include_bytes!("../../assets/fonts/NotoSansMono-Regular.ttf");
+const NOTO_SANS_MONO_BOLD: &[u8] = include_bytes!("../../assets/fonts/NotoSansMono-Bold.ttf");
+
+/// What starting up found about text rendering, for the on-screen
+/// Diagnostics page and the one startup log line (RUST.md's P0 box, "log
+/// once at startup ... the number of font families found, the default
+/// family resolved"). Built once by `TextData::font_diagnostics` --
+/// `Default::default` still exists for callers (tests, examples) that
+/// don't need the report.
+#[derive(Clone, Debug)]
+pub struct FontDiagnostics {
+    /// `Collection::family_names().count()` after registering the bundled
+    /// fonts -- system families plus the two bundled ones.
+    pub families_found: usize,
+    /// The family `GenericFamily::SansSerif` resolves to first -- the
+    /// bundled "Noto Sans" unless registration itself failed.
+    pub default_family: Option<String>,
+    /// The family `GenericFamily::Monospace` resolves to first.
+    pub default_mono_family: Option<String>,
+    /// One resolved family name per style axis this crate actually uses
+    /// (`SpanStyle::bold`/`italic`), so a report can say plainly whether a
+    /// bold/italic request is landing on a real face rather than being
+    /// silently absorbed by whatever the sans-serif default resolves to
+    /// for every weight (RUST.md's P0 box, "bold words render as blank
+    /// gaps" -- a family that resolves but has no distinct bold face is
+    /// exactly what produced that).
+    pub regular_resolved: Option<String>,
+    pub bold_resolved: Option<String>,
+    pub italic_resolved: Option<String>,
+    pub mono_resolved: Option<String>,
+}
+
 /// Everything text needs that outlives one string: the font collection, the
 /// layout scratch space, the glyph rasteriser and the atlas they fill.
 pub struct TextData {
@@ -17,15 +66,182 @@ pub struct TextData {
     pub layout_cx: LayoutContext<UiColor>,
     scale_cx: ScaleContext,
     pub atlas: GlyphAtlas,
+    /// Physical pixels per dp -- a second copy of
+    /// `UiRenderState::density`, kept here too because `TextEditCtx::layout`
+    /// (cursor movement and hit-testing, `widget/text/edit.rs`) shapes text
+    /// from an event callback that has a `TextData` but no `Painter`, so it
+    /// has nowhere else to read the display's density from. Both copies are
+    /// set together, from the one place either backend learns the real
+    /// value (`android::view::new_peer`); this is the same accepted
+    /// duplication as `AndroidRenderer::content_scale`; a single source of
+    /// truth would mean carrying a `Painter` (or output size) into every
+    /// input handler for the sake of one field.
+    pub density: f32,
 }
 
 impl Default for TextData {
     fn default() -> Self {
-        Self {
+        let mut data = Self {
             font_cx: FontContext::new(),
             layout_cx: LayoutContext::new(),
             scale_cx: ScaleContext::new(),
             atlas: GlyphAtlas::default(),
+            density: 1.0,
+        };
+        data.register_bundled_fonts();
+        data
+    }
+}
+
+impl TextData {
+    /// Registers Noto Sans (regular/bold/italic/bold-italic) and Noto Sans
+    /// Mono (regular/bold) as static faces, and puts them **first** in the
+    /// `SansSerif`/`Monospace` generic-family fallback lists -- ahead of,
+    /// not instead of, whatever the platform already found, so a script
+    /// Noto Sans lacks (CJK, emoji, ...) still falls through to the system
+    /// font the same as before this existed.
+    ///
+    /// Exists because text rendering must not depend on the platform's own
+    /// font enumeration succeeding or resolving weight/style the way this
+    /// crate assumes: RUST.md's P0 box found bold spans on a real phone
+    /// rendering as blank gaps of the correct advance width (the glyph
+    /// simply wasn't rasterised -- `TextData::place`'s `None` arm), while
+    /// the emulator's system fonts happened to resolve every style. A
+    /// bundled, static-per-style family removes fontique's Android font
+    /// scan (`fontique::backend::android::SystemFonts::new`, which parses
+    /// `/system/fonts` and `/system/etc/fonts.xml`) from the path a glyph
+    /// has to survive to reach the screen at all.
+    ///
+    /// Cost: six static `.ttf`s, ~3.6 MB uncompressed
+    /// (`iris/core/assets/fonts/`), landing in the APK compressed --
+    /// `build-apk.sh`'s own output is what says the delivered number, not
+    /// this comment.
+    fn register_bundled_fonts(&mut self) {
+        fn register(cx: &mut FontContext, bytes: &'static [u8]) -> Option<FamilyId> {
+            let blob = Blob::new(Arc::new(bytes));
+            cx.collection
+                .register_fonts(blob, None)
+                .into_iter()
+                .map(|(id, _)| id)
+                .next()
+        }
+        let sans_id = register(&mut self.font_cx, NOTO_SANS_REGULAR);
+        register(&mut self.font_cx, NOTO_SANS_BOLD);
+        register(&mut self.font_cx, NOTO_SANS_ITALIC);
+        register(&mut self.font_cx, NOTO_SANS_BOLD_ITALIC);
+        let mono_id = register(&mut self.font_cx, NOTO_SANS_MONO_REGULAR);
+        register(&mut self.font_cx, NOTO_SANS_MONO_BOLD);
+
+        if let Some(sans_id) = sans_id {
+            let existing: Vec<_> = self
+                .font_cx
+                .collection
+                .generic_families(GenericFamily::SansSerif)
+                .collect();
+            self.font_cx.collection.set_generic_families(
+                GenericFamily::SansSerif,
+                std::iter::once(sans_id).chain(existing),
+            );
+            let existing: Vec<_> = self
+                .font_cx
+                .collection
+                .generic_families(GenericFamily::SystemUi)
+                .collect();
+            self.font_cx.collection.set_generic_families(
+                GenericFamily::SystemUi,
+                std::iter::once(sans_id).chain(existing),
+            );
+        }
+        if let Some(mono_id) = mono_id {
+            let existing: Vec<_> = self
+                .font_cx
+                .collection
+                .generic_families(GenericFamily::Monospace)
+                .collect();
+            self.font_cx.collection.set_generic_families(
+                GenericFamily::Monospace,
+                std::iter::once(mono_id).chain(existing),
+            );
+        }
+    }
+
+    /// Builds the startup report -- see `FontDiagnostics`. Queries the
+    /// collection directly (`fontique::Query`) rather than shaping a real
+    /// string, since all that's needed is which family each axis lands on.
+    pub fn font_diagnostics(&mut self) -> FontDiagnostics {
+        use parley::fontique::{Attributes, FontWidth, QueryStatus};
+        let families_found = self.font_cx.collection.family_names().count();
+        let default_family_id = self
+            .font_cx
+            .collection
+            .generic_families(GenericFamily::SansSerif)
+            .next();
+        let default_family = default_family_id
+            .and_then(|id| self.font_cx.collection.family_name(id).map(str::to_string));
+        let default_mono_family_id = self
+            .font_cx
+            .collection
+            .generic_families(GenericFamily::Monospace)
+            .next();
+        let default_mono_family = default_mono_family_id
+            .and_then(|id| self.font_cx.collection.family_name(id).map(str::to_string));
+
+        // Resolves the family a (generic family, weight, style) query lands
+        // on, without holding the `Query`'s borrow of `collection` across
+        // the `family_name` lookup that needs it back -- the `FamilyId` is
+        // captured out of the closure first, then looked up once `query`
+        // (and its borrow) has been dropped.
+        let mut resolve_family =
+            |generic: GenericFamily, weight: FontWeight, style: FontStyle| -> Option<String> {
+                let mut family_id = None;
+                {
+                    let mut query = self
+                        .font_cx
+                        .collection
+                        .query(&mut self.font_cx.source_cache);
+                    query.set_families([generic]);
+                    query.set_attributes(Attributes {
+                        width: FontWidth::NORMAL,
+                        style,
+                        weight,
+                    });
+                    query.matches_with(|font| {
+                        family_id = Some(font.family.0);
+                        QueryStatus::Stop
+                    });
+                }
+                family_id.and_then(|id| self.font_cx.collection.family_name(id).map(str::to_string))
+            };
+
+        let regular_resolved = resolve_family(
+            GenericFamily::SansSerif,
+            FontWeight::NORMAL,
+            FontStyle::Normal,
+        );
+        let bold_resolved = resolve_family(
+            GenericFamily::SansSerif,
+            FontWeight::BOLD,
+            FontStyle::Normal,
+        );
+        let italic_resolved = resolve_family(
+            GenericFamily::SansSerif,
+            FontWeight::NORMAL,
+            FontStyle::Italic,
+        );
+        let mono_resolved = resolve_family(
+            GenericFamily::Monospace,
+            FontWeight::NORMAL,
+            FontStyle::Normal,
+        );
+
+        FontDiagnostics {
+            families_found,
+            default_family,
+            default_mono_family,
+            regular_resolved,
+            bold_resolved,
+            italic_resolved,
+            mono_resolved,
         }
     }
 }
@@ -159,7 +375,7 @@ pub struct TextBuffer {
     /// `set_spans` forces `shaped` to `None` directly, the same way `edit`
     /// does, since spans change far less often than a naive equality check
     /// on the whole `Vec` would cost to compute every frame.
-    shaped: Option<(TextAttrs, Option<f32>)>,
+    shaped: Option<(TextAttrs, Option<f32>, f32)>,
 }
 
 impl TextBuffer {
@@ -215,19 +431,42 @@ impl TextBuffer {
         Vec2::new(self.layout.width(), self.layout.height())
     }
 
-    /// Lay the text out, unless it is already laid out for these attributes and
+    /// Lay the text out, unless it is already laid out for these
-    /// this width.
+    /// attributes, this width and this density.
-    pub fn shape(&mut self, data: &mut TextData, attrs: &TextAttrs, width: Option<f32>) {
+    ///
-        if self.shaped.as_ref() == Some(&(attrs.clone(), width)) {
+    /// **`attrs.font_size`/`line_height` and every span's own `font_size`
+    /// are density-independent (dp) units, multiplied by `density` here --
+    /// the one place text crosses from the widget tree's dp sizes into the
+    /// physical pixels the shaper and rasteriser (`TextData::place`) both
+    /// then work in.** This is what makes glyphs sharp on a dense display:
+    /// before this existed, `font_size` was already a physical-pixel value
+    /// (RUST.md's P0 box's global-scale stopgap resolved density by
+    /// stretching the whole rendered frame afterward instead), so a glyph
+    /// was rasterised small and then upscaled by whatever the display's
+    /// scale factor was -- exactly the blur Iris's report described.
+    /// Multiplying here instead means the font size hitting `ScaleContext`
+    /// in `place` below is already the display's real physical size, so
+    /// the atlas holds a bitmap at the resolution it is actually shown at.
+    /// `GlyphKey.size` already keys on that resolved `font_size`
+    /// (`(font_size * 16.0).round()`), so a cache entry is naturally per
+    /// physical size with no change needed there.
+    pub fn shape(
+        &mut self,
+        data: &mut TextData,
+        attrs: &TextAttrs,
+        width: Option<f32>,
+        density: f32,
+    ) {
+        if self.shaped.as_ref() == Some(&(attrs.clone(), width, density)) {
             return;
         }
         let mut builder = data
             .layout_cx
             .ranged_builder(&mut data.font_cx, &self.text, 1.0, true);
         builder.push_default(StyleProperty::FontFamily(attrs.family.family()));
-        builder.push_default(StyleProperty::FontSize(attrs.font_size));
+        builder.push_default(StyleProperty::FontSize(attrs.font_size * density));
         builder.push_default(StyleProperty::LineHeight(LineHeight::Absolute(
-            attrs.line_height,
+            attrs.line_height * density,
         )));
         builder.push_default(StyleProperty::Brush(attrs.color));
         for span in &self.spans {
@@ -239,7 +478,7 @@ impl TextBuffer {
                 builder.push(StyleProperty::FontFamily(family.family()), range.clone());
             }
             if let Some(size) = span.font_size {
-                builder.push(StyleProperty::FontSize(size), range.clone());
+                builder.push(StyleProperty::FontSize(size * density), range.clone());
             }
             if span.bold {
                 builder.push(StyleProperty::FontWeight(FontWeight::BOLD), range.clone());
@@ -255,7 +494,7 @@ impl TextBuffer {
         self.layout.break_all_lines(width);
         self.layout
             .align(Alignment::Start, AlignmentOptions::default());
-        self.shaped = Some((attrs.clone(), width));
+        self.shaped = Some((attrs.clone(), width, density));
     }
 }
 
@@ -372,8 +611,9 @@ impl TextData {
         attrs: &TextAttrs,
         width: Option<f32>,
         textures: &mut Textures,
+        density: f32,
     ) -> RenderedText {
-        buffer.shape(self, attrs, width);
+        buffer.shape(self, attrs, width, density);
         let glyphs = self.place(buffer, textures);
         RenderedText {
             glyphs: std::sync::Arc::new(glyphs),

iris/core/src/render/mod.rs

@@ -4,6 +4,7 @@ use crate::{
     util::{HashMap, Vec2},
 };
 use data::WindowUniform;
+use pollster::FutureExt;
 use wgpu::{
     util::{BufferInitDescriptor, DeviceExt},
     *,
@@ -65,6 +66,57 @@ pub fn device_limits() -> Limits {
     }
 }
 
+/// A capped log of wgpu's *uncaptured* errors -- everything that reaches
+/// `Device::on_uncaptured_error` rather than one of `UiRenderNode::new`'s
+/// own error scopes, i.e. every wgpu error raised outside device/pipeline
+/// creation: a validation failure during an ordinary frame's `update`/
+/// `draw`, for instance. wgpu's default handler for these is `panic!` with
+/// no caller able to intervene -- exactly what aborted the P0 bench APK
+/// once already (this file's `UiRenderNode::new` doc comment) -- so both
+/// platform backends install a handler here instead of leaving the default
+/// in place, per RUST.md's P0 box ("every wgpu uncaptured error ... it
+/// must never panic in release").
+///
+/// Cheap to `Clone` (an `Arc` around the real storage) rather than a
+/// process-wide static, so a caller builds one alongside its `Device`,
+/// hands one clone to `on_uncaptured_error`'s closure and keeps the other
+/// for the Diagnostics page to read -- context passed explicitly, per
+/// AGENTS.md/CODE_RULES.md's "no globals" rather than reached for through a
+/// `OnceLock`.
+#[derive(Clone)]
+pub struct WgpuErrorLog {
+    errors: std::sync::Arc<std::sync::Mutex<std::collections::VecDeque<String>>>,
+}
+
+/// How many uncaptured errors the log keeps -- old ones drop off the front
+/// rather than being trimmed on read, so a build spraying errors every
+/// frame doesn't grow this without bound.
+const WGPU_ERROR_LOG_CAP: usize = 20;
+
+impl Default for WgpuErrorLog {
+    fn default() -> Self {
+        Self {
+            errors: std::sync::Arc::new(std::sync::Mutex::new(std::collections::VecDeque::new())),
+        }
+    }
+}
+
+impl WgpuErrorLog {
+    pub fn record(&self, error: impl std::fmt::Display) {
+        let mut errors = self.errors.lock().unwrap();
+        if errors.len() >= WGPU_ERROR_LOG_CAP {
+            errors.pop_front();
+        }
+        errors.push_back(error.to_string());
+    }
+
+    /// A snapshot for the Diagnostics page -- cloned rather than held,
+    /// since the lock must not outlive one call.
+    pub fn snapshot(&self) -> Vec<String> {
+        self.errors.lock().unwrap().iter().cloned().collect()
+    }
+}
+
 pub struct UiRenderNode {
     uniform_group: BindGroup,
     primitive_layout: BindGroupLayout,
@@ -152,7 +204,7 @@ impl UiRenderNode {
         queue: &Queue,
         ui: &mut UiData,
         ui_render: &mut UiRenderState,
-    ) {
+    ) -> FrameUpdateStats {
         self.active.clear();
         for (i, primitives) in ui_render.layers.iter_mut() {
             self.active.push(i);
@@ -236,6 +288,10 @@ impl UiRenderNode {
         if rebuild_main {
             self.rsc_group = Self::rsc_group(device, &self.rsc_layout, &self.textures);
         }
+        FrameUpdateStats {
+            masks_resized,
+            moves_resized,
+        }
     }
 
     /// Takes a size rather than a window type: this is the only thing the
@@ -251,26 +307,69 @@ impl UiRenderNode {
         queue.write_buffer(&self.window_buffer, 0, bytemuck::cast_slice(slice));
     }
 
-    pub fn new(device: &Device, queue: &Queue, config: &SurfaceConfiguration) -> Self {
+    /// Builds every bind group layout, the pipeline, and the two storage
+    /// buffers this needs -- fallibly, since this is exactly the call that
+    /// aborted the process on Iris's phone in a release build with no
+    /// message beyond "wgpu error: Validation Error" (RUST.md's P0 box,
+    /// "iris bench crash on the phone, 2026-09-06"). wgpu's own default
+    /// behaviour for an uncaptured error is `panic!` with no caller able to
+    /// intervene, so every `create_bind_group_layout`/`create_render_pipeline`
+    /// call below runs inside three nested error scopes (one per
+    /// `ErrorFilter`) instead: whichever scope catches something, its
+    /// `wgpu::Error`'s `Display` is wgpu-core's own `format_error` output
+    /// (`"Validation Error\n\nCaused by:\n  ..."`, the same text the panic
+    /// would have printed before Android's crash reporter truncated it) and
+    /// becomes this function's `Err`. Both callers
+    /// (`android::render::AndroidRenderer::new`, `default::render::
+    /// UiRenderer::new`) already call `Device`-creation with
+    /// `pollster::block_on`, so returning a plain `Result` here rather than
+    /// making this `async fn` keeps that same synchronous shape.
+    pub fn new(
+        device: &Device,
+        queue: &Queue,
+        config: &SurfaceConfiguration,
+        window_size: impl Into<Vec2>,
+    ) -> Result<Self, String> {
+        // Popped in reverse of this order, once every creation call below
+        // has run -- `Device::push_error_scope`'s own contract.
+        let oom_scope = device.push_error_scope(ErrorFilter::OutOfMemory);
+        let validation_scope = device.push_error_scope(ErrorFilter::Validation);
+        let internal_scope = device.push_error_scope(ErrorFilter::Internal);
+
         let shader = device.create_shader_module(ShaderModuleDescriptor {
             label: Some("UI Shape Shader"),
             source: ShaderSource::Wgsl(SHAPE_SHADER.into()),
         });
 
-        // Seeded from the surface's own size, not `WindowUniform::default()`
+        // Seeded from the caller's own reported size, not
-        // (0, 0): the vertex shader divides by `window.dim` to reach clip
+        // `WindowUniform::default()` (0, 0): the vertex shader divides by
-        // space, so a window this buffer disagrees with means every
+        // `window.dim` to reach clip space, so a window this buffer
-        // primitive's position is NaN/Inf and is dropped before
+        // disagrees with means every primitive's position is NaN/Inf and is
-        // rasterization -- the clear colour still reaches the screen (the
+        // dropped before rasterization -- the clear colour still reaches
-        // pass runs regardless) while nothing drawn on top of it ever does.
+        // the screen (the pass runs regardless) while nothing drawn on top
-        // winit's backend gets away with the old default because winit
+        // of it ever does. winit's backend gets away with the old default
-        // fires an initial `WindowEvent::Resized` that calls `resize()`
+        // because winit fires an initial `WindowEvent::Resized` that calls
-        // before the first frame; android-view has no such automatic
+        // `resize()` before the first frame; android-view has no such
-        // event, so `AndroidRenderer::new` built a node whose window buffer
+        // automatic event, so `AndroidRenderer::new` built a node whose
-        // was never corrected -- this is I2's "nothing draws" bug (RUST.md).
+        // window buffer was never corrected -- this is I2's "nothing draws"
-        let window_uniform = WindowUniform {
+        // bug (RUST.md).
-            width: config.width as f32,
+        //
-            height: config.height as f32,
+        // **Deliberately not `config.width`/`config.height`**: those are
+        // the surface's *physical* pixel size, which the swapchain needs,
+        // but everything downstream of this uniform (layout, hit-testing,
+        // glyph/rect positions) works in the caller's own units -- on
+        // Android that's *logical* (physical / density) since RUST.md's P0
+        // box ("text is far too small"), on desktop it's whatever
+        // `default::render::UiRenderer::new` already divides by
+        // `window.scale_factor()`. Passing it in explicitly, rather than
+        // deriving it from `config` here, is what keeps this crate from
+        // needing to know either platform's notion of density at all.
+        let window_uniform = {
+            let size = window_size.into();
+            WindowUniform {
+                width: size.x,
+                height: size.y,
+            }
         };
         let window_buffer = device.create_buffer_init(&BufferInitDescriptor {
             label: Some("window"),
@@ -373,7 +472,18 @@ impl UiRenderNode {
             cache: None,
         });
 
-        Self {
+        // Reverse of the push order above. Only one of these should ever be
+        // `Some` in practice -- three separate scopes exist to name *which*
+        // kind of error it was, not because more than one is expected at
+        // once.
+        let internal_err = internal_scope.pop().block_on();
+        let validation_err = validation_scope.pop().block_on();
+        let oom_err = oom_scope.pop().block_on();
+        if let Some(err) = validation_err.or(oom_err).or(internal_err) {
+            return Err(err.to_string());
+        }
+
+        Ok(Self {
             uniform_group,
             primitive_layout,
             rsc_layout,
@@ -387,7 +497,7 @@ impl UiRenderNode {
             move_offsets,
             masks_layout,
             masks_group,
-        }
+        })
     }
 
     fn bind_group_0(
@@ -554,4 +664,26 @@ impl UiRenderNode {
     pub fn take_image_bind_group_creates(&mut self) -> u64 {
         self.textures.take_bind_group_creates()
     }
+
+    /// Atlas-array `grow_array` calls since the last call -- same calling
+    /// convention as `take_image_bind_group_creates` (call once per frame,
+    /// before `update()`, to read exactly the previous frame's tally). Part
+    /// of the Diagnostics page's per-frame report (RUST.md's P0 box, "the
+    /// first input frame" investigation): if a report ever shows a grow
+    /// landing on the same frame the glyphs vanished, that is the
+    /// coincidence to chase first.
+    pub fn take_atlas_pages_grown(&mut self) -> u64 {
+        self.textures.take_pages_grown()
+    }
+}
+
+/// What `UiRenderNode::update` changed this frame that a caller building a
+/// per-frame diagnostic report cares about -- see `take_image_bind_group_creates`/
+/// `take_atlas_pages_grown` for the two counters this doesn't carry (they
+/// use the existing "call before update()" convention instead, so as not
+/// to disturb `bench_images`' documented counts).
+#[derive(Clone, Copy, Debug, Default)]
+pub struct FrameUpdateStats {
+    pub masks_resized: bool,
+    pub moves_resized: bool,
 }

iris/core/src/render/texture.rs

@@ -67,6 +67,12 @@ pub struct GpuTextures {
     /// unchanging image list is zero, the same way `UiRenderState`'s
     /// `draw_count`/`region_mut_count` prove the layout side.
     bind_group_creates: u64,
+    /// `grow_array` calls since the last `take_pages_grown` -- the
+    /// Diagnostics page's per-frame report (RUST.md's P0 box, "the first
+    /// input frame" investigation) reads this alongside `bind_group_creates`
+    /// to say whether *this* frame's glyph disappearance, if any, coincided
+    /// with the atlas array being recreated.
+    pages_grown: u64,
 }
 
 impl GpuTextures {
@@ -226,6 +232,7 @@ impl GpuTextures {
     /// array's view, which invalidates every bind group that referenced it,
     /// so this also rebuilds all of them before returning.
     fn grow_array(&mut self, rsc_layout: &BindGroupLayout) {
+        self.pages_grown += 1;
         let new_capacity = self.array_capacity * 2;
         let new_texture = Self::create_array_texture(&self.device, new_capacity);
         if self.page_count > 0 {
@@ -392,6 +399,7 @@ impl GpuTextures {
             sampler,
             null_view,
             bind_group_creates: 0,
+            pages_grown: 0,
         }
     }
 
@@ -402,6 +410,12 @@ impl GpuTextures {
         std::mem::take(&mut self.bind_group_creates)
     }
 
+    /// Reads and zeroes the atlas-array-grow counter -- see `pages_grown`'s
+    /// field comment.
+    pub fn take_pages_grown(&mut self) -> u64 {
+        std::mem::take(&mut self.pages_grown)
+    }
+
     pub fn array_view(&self) -> &TextureView {
         &self.array_view
     }

iris/core/src/ui/painter.rs

@@ -165,8 +165,10 @@ impl<'a> Painter<'a> {
         attrs: &TextAttrs,
         width: Option<f32>,
     ) -> RenderedText {
+        let density = self.state.density;
         let ui = self.rsc.ui_mut();
-        ui.text.render(buffer, attrs, width, &mut ui.textures)
+        ui.text
+            .render(buffer, attrs, width, &mut ui.textures, density)
     }
 
     /// Draw a laid-out string: one quad per glyph, all sampling the atlas.
@@ -210,6 +212,12 @@ impl<'a> Painter<'a> {
         self.state.output_size
     }
 
+    /// Physical pixels per `dp` -- see `UiRenderState::density`'s field
+    /// doc. What `Len::dp`'s `apply_rest` call resolves against.
+    pub fn density(&self) -> f32 {
+        self.state.density
+    }
+
     pub fn px_size(&mut self) -> Vec2 {
         self.region.size().to_abs(self.state.output_size)
     }

iris/core/src/ui/render_state.rs

@@ -9,6 +9,12 @@ pub struct UiRenderState {
     pub active: HashMap<WidgetId, ActiveData>,
     pub layers: PrimitiveLayers,
     pub(super) output_size: Vec2,
+    /// Physical pixels per `dp` -- see `Len::dp`'s field doc. `1.0` (an
+    /// unscaled display) until a backend that knows its own density calls
+    /// `set_density` (Android's `content_scale`, read at `surface_changed`
+    /// time); the winit backend has no analogous per-monitor value wired up
+    /// yet and stays at the default.
+    pub(super) density: f32,
 
     old_root: Option<WidgetId>,
     resized: bool,
@@ -35,6 +41,7 @@ impl UiRenderState {
             active: Default::default(),
             layers: Default::default(),
             output_size: Vec2::ZERO,
+            density: 1.0,
             old_root: None,
             resized: false,
             draw_started: Default::default(),
@@ -60,6 +67,20 @@ impl UiRenderState {
         self.resized = true;
     }
 
+    /// Sets the physical-pixels-per-dp ratio every `Len::dp` in the tree
+    /// resolves against from the next layout pass on -- see `density`'s
+    /// field doc. Not folded into `resize` because the two change on
+    /// different triggers (a surface resize on every rotation or keyboard
+    /// open; a density change only if the app follows the display to a
+    /// different screen, which Android surfaces separately).
+    pub fn set_density(&mut self, density: f32) {
+        self.density = density;
+    }
+
+    pub fn density(&self) -> f32 {
+        self.density
+    }
+
     pub fn update<'a>(&mut self, root: impl Into<Option<&'a StrongWidget>>, rsc: &mut dyn UiRsc) {
         // safety mechanism for memory leaks; might wanna return a result instead so user can
         // decide whether to panic or not
@@ -311,7 +332,7 @@ impl UiRenderState {
         };
         let from = active
             .size
-            .to_uivec2()
+            .to_uivec2(self.density)
             .align(RegionAlign::TOP_LEFT)
             .within(&active.region);
         let slot = active.move_slot;

iris/desktop-app/src/app.rs

@@ -15,23 +15,19 @@
 //! +-----------+--------------------------------------+
 //! ```
 //!
-//! **Deliberately left simple, and why**: every incoming SSE event refolds
+//! **Incoming SSE events go through `TranscriptScreen::apply`**, not a
-//! the *entire* transcript (`client_core::transcript_fold::fold_event` is
+//! full rebuild: `client_core::transcript_fold::fold_event` folds the new
-//! already `O(items)` and a desktop session's conversation is small) and
+//! item list as before, then `apply` updates only the row(s) that actually
-//! rebuilds the whole right-hand widget tree from scratch, rather than
+//! changed (almost always the one still-open assistant message a delta
-//! reaching for `TranscriptScreen::push_row`'s incremental append.
+//! landed in) instead of rebuilding the whole right-hand widget tree from
-//! `push_row` cannot update a row already on screen -- only append a new
+//! scratch. `rebuild_transcript` still runs the whole tree once, for a
-//! one -- and a streaming assistant reply is exactly a row whose *text*
+//! freshly loaded/selected session and for `apply`'s own rare
-//! keeps changing after it first appears (see `transcript-ui`'s own doc on
+//! full-rebuild fallback (a `group_tool_runs` regroup touching a row
-//! `fold_event` folding deltas into one growing item). A full rebuild
+//! before the tail). The composer's in-progress text survives a rebuild
-//! shows that growth correctly at the cost of redrawing everything each
+//! (`rebuild_transcript`'s `in_progress` local) since the user typing a
-//! time; fine for this proof, wrong for a long, fast-streaming transcript
+//! followup while a reply streams in is the one case a naive rebuild
-//! -- the incremental path that fixes it needs `transcript-ui` to expose
+//! would otherwise lose data on -- `apply`'s own path never touches the
-//! updating a row in place, which it does not yet. The composer's
+//! composer at all, so this only matters on the fallback.
-//! in-progress text survives a rebuild (`rebuild_transcript`'s
-//! `in_progress` local) since the user typing a followup while a reply
-//! streams in is the one case a naive rebuild would otherwise lose data
-//! on.
 //!
 //! Background network I/O (`client_core::api`/`event_stream`, both
 //! blocking by design -- see `client-core`'s `Cargo.toml`) runs on plain
@@ -209,8 +205,12 @@ impl DefaultAppState for Client {
                 event,
             } => {
                 if self.current(&session_id, generation) {
+                    let old_items = self.items.clone();
                     self.items = fold_event(&self.items, &event);
-                    self.rebuild_transcript(rsc);
+                    match &self.screen {
+                        Some(screen) => screen.apply(rsc, &old_items, &self.items),
+                        None => self.rebuild_transcript(rsc),
+                    }
                 }
             }
             AppEvent::StreamEnded {

iris/examples/message_list.rs

@@ -68,12 +68,15 @@ fn build_row<Rsc: UiRsc + 'static>(rsc: &mut Rsc, i: usize) -> StrongWidget {
         let mut span = Span::empty(Dir::DOWN);
         span.push(text);
         span.push(img);
-        span.pad(8.0).background(rect(tint)).add_strong(rsc).any()
+        span.pad(dp(8.0))
+            .background(rect(tint))
+            .add_strong(rsc)
+            .any()
     } else {
         wtext(row_text(i))
             .wrap(true)
             .color(text_color)
-            .pad(8.0)
+            .pad(dp(8.0))
             .background(rect(tint))
             .add_strong(rsc)
             .any()

iris/src/android/mod.rs

@@ -23,7 +23,8 @@ mod view;
 pub use insets::Insets;
 pub use render::AndroidRenderer;
 pub use view::{
-    AndroidAppState, AndroidRsc, AndroidUiState, HasAndroidUiState, IrisViewPeer, new_peer,
+    AndroidAppState, AndroidRsc, AndroidUiState, HasAndroidUiState, IrisViewPeer, WindowInsets,
+    new_peer,
 };
 
 /// Registers the extra native methods this backend needs beyond what

iris/src/android/render.rs

@@ -48,10 +48,65 @@ pub struct AndroidRenderer {
     config: SurfaceConfiguration,
     encoder: CommandEncoder,
     pub ui: UiRenderNode,
+    /// The adapter identity, kept past `new()` for the Diagnostics page --
+    /// `Adapter` itself is not `Clone`, so the three fields the page shows
+    /// are copied out once here rather than holding the adapter.
+    pub adapter_name: String,
+    pub adapter_backend: Backend,
+    pub adapter_driver: String,
+    /// Every uncaptured wgpu error since this renderer was created -- see
+    /// `iris_core::WgpuErrorLog`'s doc comment. Installed on `device` in
+    /// `new()`, kept here so the Diagnostics page and the per-frame log in
+    /// `update()` can both read it without a global.
+    pub wgpu_errors: iris_core::WgpuErrorLog,
+    /// Frames drawn on this surface -- what gates the first-10-frames log
+    /// `update()` writes (RUST.md's P0 box, "the first input frame"
+    /// investigation): a fresh surface is exactly what Iris's own report
+    /// says renders correctly at first, so the frames that matter are the
+    /// first several after each `surface_changed`, not an arbitrary window
+    /// during a long-running session.
+    frame_count: u64,
+    /// Physical pixels per dp -- see `android::view::AndroidUiState::
+    /// content_scale`'s field comment for what this feeds.
+    content_scale: f32,
+}
+
+/// One frame's worth of the counters `render/mod.rs`'s doc comments on
+/// `FrameUpdateStats`/`take_image_bind_group_creates`/
+/// `take_atlas_pages_grown` describe -- assembled here because the three
+/// live on two different calling conventions (`FrameUpdateStats` from this
+/// exact `update()` call; the other two describe the *previous* frame,
+/// same as `bench_images`' existing use of them) and a diagnostic reader
+/// should not have to know that split.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct FrameDiagnostics {
+    pub masks_resized: bool,
+    pub moves_resized: bool,
+    /// From the previous frame's `update()` -- see the struct doc.
+    pub atlas_pages_grown_prev: u64,
+    pub image_bind_group_creates_prev: u64,
 }
 
 impl AndroidRenderer {
-    pub fn new(window: NativeWindow, width: u32, height: u32) -> Self {
+    /// `Err` holds a full, human-readable report -- wgpu's own error text
+    /// (`UiRenderNode::new`'s doc comment) plus the adapter identity and
+    /// the limits/downlevel flags bind-group-layout validation checks
+    /// against -- rather than the panic wgpu's default error handler would
+    /// otherwise raise with no caller able to see it. This is what aborted
+    /// the P0 bench APK on Iris's phone with only "wgpu error: Validation
+    /// Error" surviving into the crash report (RUST.md's P0 box, "iris
+    /// bench crash on the phone, 2026-09-06"): `create_bind_group_layout`
+    /// validates against *this* adapter's downlevel capabilities and
+    /// limits, which a desktop GPU and the emulator's software renderers
+    /// never exercised. The caller (`android::view::IrisViewPeer::
+    /// surface_changed`) logs this one-line-flattened and shows it on
+    /// screen instead of aborting the process.
+    pub fn new(
+        window: NativeWindow,
+        width: u32,
+        height: u32,
+        content_scale: f32,
+    ) -> Result<Self, String> {
         // `force-gles` (RUST.md's I5 "Where iris's frame time goes") swaps
         // the software-Vulkan (SwiftShader) path for GLES/virgl on the same
         // build, to isolate whether the backend itself explains the frame
@@ -84,6 +139,18 @@ impl AndroidRenderer {
             .block_on()
             .expect("Could not get adapter!");
 
+        // Requesting the device itself still panics on failure: that is a
+        // `RequestDeviceError` (a limit or feature the adapter cannot grant
+        // at all), a different and already-diagnosable failure from the one
+        // this function now recovers from -- `RUST.md`'s "Software mode ...
+        // crashes for a third, different reason" is exactly that class, and
+        // its message already names the limit and the requested/allowed
+        // values with no truncation risk (it never reaches wgpu's
+        // uncaptured-error path). What this function's `Result` return
+        // covers is the *next* class of failure: the adapter grants the
+        // device, and validation only fails once a specific bind group
+        // layout is checked against it.
+
         // Same request as the winit backend's `UiRenderer::new` -- no
         // binding-array features, see TEXTURES.md's "Recommended shape".
         // `iris_core::device_limits()` is shared between the two backends;
@@ -96,6 +163,30 @@ impl AndroidRenderer {
             .block_on()
             .expect("Could not get device!");
 
+        // wgpu's default handler for an error raised outside `UiRenderNode::
+        // new`'s own error scopes (i.e. everything past device creation --
+        // an ordinary frame's `update`/`draw`) is `panic!`, unconditionally,
+        // with no caller able to intervene: the same mechanism that aborted
+        // the P0 bench APK once already, just at a different call site. Log
+        // and record instead of letting that default stand -- RUST.md's P0
+        // box, "every wgpu uncaptured error ... it must never panic in
+        // release".
+        let wgpu_errors = iris_core::WgpuErrorLog::default();
+        let wgpu_errors_for_handler = wgpu_errors.clone();
+        device.on_uncaptured_error(std::sync::Arc::new(move |error| {
+            log::error!("iris wgpu uncaptured error: {error}");
+            wgpu_errors_for_handler.record(error);
+        }));
+
+        let info = adapter.get_info();
+        let adapter_name = info.name.clone();
+        let adapter_backend = info.backend;
+        let adapter_driver = if info.driver_info.is_empty() {
+            info.driver.clone()
+        } else {
+            format!("{} {}", info.driver, info.driver_info)
+        };
+
         let surface_caps = surface.get_capabilities(&adapter);
         let surface_format = surface_caps
             .formats
@@ -117,16 +208,121 @@ impl AndroidRenderer {
         surface.configure(&device, &config);
 
         let encoder = Self::create_encoder(&device);
-        let ui = UiRenderNode::new(&device, &queue, &config);
+        // Physical pixels, matching the swapchain's own `width`/`height`
+        // exactly -- see `android::view::AndroidUiState::content_scale`'s
+        // field comment for why this is no longer divided into a separate
+        // logical space (that stopgap is what made text blurry, RUST.md's
+        // P0 box). `Len::dp` folds the density in at layout time instead,
+        // so nothing here needs to know it at all.
+        let window_size = iris_core::util::Vec2::new(width as f32, height as f32);
+        let ui = match UiRenderNode::new(&device, &queue, &config, window_size) {
+            Ok(ui) => ui,
+            Err(wgpu_error) => return Err(Self::diagnostic(&adapter, &wgpu_error)),
+        };
 
-        Self {
+        Ok(Self {
             surface,
             device,
             queue,
             config,
             encoder,
             ui,
+            adapter_name,
+            adapter_backend,
+            adapter_driver,
+            wgpu_errors,
+            frame_count: 0,
+            content_scale,
+        })
     }
+
+    /// The adapter identity plus every limit and downlevel flag
+    /// `create_bind_group_layout` validates a storage buffer or texture
+    /// binding against, followed by wgpu's own error text -- everything a
+    /// person reading this off a screenshot needs to tell "this adapter
+    /// lacks X" from "this is a bug in the layout." Named explicitly rather
+    /// than `{limits:?}`/`{flags:?}` wholesale, because `Limits` alone is
+    /// dozens of fields nobody asked for -- these are exactly the ones
+    /// `UiRenderNode::new`'s layouts (`rsc_layout`, `masks_layout`,
+    /// `primitive_layout`) can fail against, per `CreateBindGroupLayoutError`
+    /// (`wgpu-core::binding_model`) and its downlevel-flag checks
+    /// (`wgpu-core::device::resource`, `VERTEX_STORAGE` in particular --
+    /// the one storage buffer here, `move_offsets`, that is visible to the
+    /// vertex stage).
+    fn diagnostic(adapter: &Adapter, wgpu_error: &str) -> String {
+        let info = adapter.get_info();
+        let limits = adapter.limits();
+        let downlevel = adapter.get_downlevel_capabilities();
+        format!(
+            "iris could not start rendering. Copy this text and send it to Iris.\n\n\
+             adapter: {name} ({backend:?}), driver: {driver} {driver_info}\n\
+             limits: max_storage_buffers_per_shader_stage={max_storage_buffers} \
+             max_sampled_textures_per_shader_stage={max_sampled_textures} \
+             max_bind_groups={max_bind_groups} \
+             max_bindings_per_bind_group={max_bindings} \
+             max_storage_buffer_binding_size={max_storage_binding} \
+             min_storage_buffer_offset_alignment={min_storage_align}\n\
+             downlevel flags: {flags:?}\n\n\
+             {wgpu_error}",
+            name = info.name,
+            backend = info.backend,
+            driver = info.driver,
+            driver_info = info.driver_info,
+            max_storage_buffers = limits.max_storage_buffers_per_shader_stage,
+            max_sampled_textures = limits.max_sampled_textures_per_shader_stage,
+            max_bind_groups = limits.max_bind_groups,
+            max_bindings = limits.max_bindings_per_bind_group,
+            max_storage_binding = limits.max_storage_buffer_binding_size,
+            min_storage_align = limits.min_storage_buffer_offset_alignment,
+            flags = downlevel.flags,
+        )
+    }
+
+    /// The Diagnostics page's whole report: adapter identity, font
+    /// resolution, the atlas's own view count, every uncaptured wgpu error
+    /// so far, and the frame report -- RUST.md's P0 box, "a named
+    /// `Diagnostics` control ... adapter info, limits, fonts found, atlas
+    /// format/pages, wgpu errors so far, frame report". One string rather
+    /// than a struct the caller formats, since the only consumer is a
+    /// plain `TextView` with a "copy this and send it to Iris" affordance,
+    /// the same shape `surface_changed`'s crash report already uses
+    /// (UI_RULES.md: a failure -- or here, a state worth reporting --
+    /// carries enough to act on where it's shown).
+    pub fn diagnostics_report(
+        &self,
+        font: &iris_core::FontDiagnostics,
+        frame_report: &str,
+    ) -> String {
+        let errors = self.wgpu_errors.snapshot();
+        let errors_text = if errors.is_empty() {
+            "none".to_string()
+        } else {
+            errors.join("\n  ")
+        };
+        format!(
+            "iris diagnostics. Copy this text and send it to Iris.\n\n\
+             adapter: {name} ({backend:?}), driver: {driver}\n\
+             content_scale: {content_scale}\n\
+             atlas format: Rgba8Unorm, views live: {views}\n\
+             fonts: {families_found} families found, default={default_family:?} \
+             mono={default_mono_family:?}\n\
+             fonts resolved: regular={regular:?} bold={bold:?} italic={italic:?} \
+             mono={mono:?}\n\
+             wgpu errors since surface creation:\n  {errors_text}\n\n\
+             {frame_report}",
+            name = self.adapter_name,
+            backend = self.adapter_backend,
+            driver = self.adapter_driver,
+            content_scale = self.content_scale,
+            views = self.ui.view_count(),
+            families_found = font.families_found,
+            default_family = font.default_family,
+            default_mono_family = font.default_mono_family,
+            regular = font.regular_resolved,
+            bold = font.bold_resolved,
+            italic = font.italic_resolved,
+            mono = font.mono_resolved,
+        )
     }
 
     fn create_encoder(device: &Device) -> CommandEncoder {
@@ -135,8 +331,31 @@ impl AndroidRenderer {
         })
     }
 
-    pub fn update(&mut self, ui: &mut UiData, render: &mut UiRenderState) {
+    /// Returns what changed this frame -- see `FrameDiagnostics`'s doc
-        self.ui.update(&self.device, &self.queue, ui, render);
+    /// comment for why two of its four fields describe the *previous*
+    /// frame rather than this one. `IrisViewPeer::render` logs this for
+    /// the first `DIAGNOSTIC_FRAMES` frames after each `surface_changed`,
+    /// per RUST.md's P0 box ("the first input frame" investigation): the
+    /// glyph-wipe Iris reported happens on the first tap or scroll after a
+    /// fresh surface, so that is exactly the window a report needs to
+    /// cover, not an arbitrary slice of a long session.
+    pub fn update(&mut self, ui: &mut UiData, render: &mut UiRenderState) -> FrameDiagnostics {
+        let atlas_pages_grown_prev = self.ui.take_atlas_pages_grown();
+        let image_bind_group_creates_prev = self.ui.take_image_bind_group_creates();
+        let stats = self.ui.update(&self.device, &self.queue, ui, render);
+        self.frame_count += 1;
+        FrameDiagnostics {
+            masks_resized: stats.masks_resized,
+            moves_resized: stats.moves_resized,
+            atlas_pages_grown_prev,
+            image_bind_group_creates_prev,
+        }
+    }
+
+    /// Frames drawn on this surface so far -- see `frame_count`'s field
+    /// comment.
+    pub fn frame_count(&self) -> u64 {
+        self.frame_count
     }
 
     /// Draws and presents one frame, returning the time spent in
@@ -179,15 +398,27 @@ impl AndroidRenderer {
         submit_start.elapsed()
     }
 
+    /// Physical pixels -- the unit layout and hit-testing use, matching
+    /// the window uniform's own units. See
+    /// `android::view::AndroidUiState::content_scale`'s field comment.
     pub fn size(&self) -> iris_core::util::Vec2 {
-        (self.config.width, self.config.height).into()
+        iris_core::util::Vec2::new(self.config.width as f32, self.config.height as f32)
     }
 
+    /// Reconfigures the surface and rewrites the window uniform for a new
+    /// physical size -- deliberately the *only* two things this does.
+    /// `device`, `ui`'s atlas, buffers and bind groups are untouched, so a
+    /// call here (as opposed to a fresh `AndroidRenderer::new`) never
+    /// invalidates a glyph the CPU-side cache already placed in the atlas.
+    /// See `android::view::IrisViewPeer::surface_changed`'s doc comment for
+    /// why that distinction matters -- it is what keeps text on screen
+    /// across an IME resize.
     pub fn resize(&mut self, width: u32, height: u32) {
         self.config.width = width;
         self.config.height = height;
         self.surface.configure(&self.device, &self.config);
-        self.ui.resize((width, height), &self.queue);
+        let size = iris_core::util::Vec2::new(width as f32, height as f32);
+        self.ui.resize(size, &self.queue);
     }
 }
 

iris/src/android/view.rs

@@ -4,7 +4,11 @@ use accesskit_android::Adapter as AccessAdapter;
 use android_view::{
     AccessibilityNodeInfo, AccessibilityNodeProvider, Bundle, CallbackCtx, Context,
     InputConnection, KeyEvent, MotionEvent, Rect, View, ViewPeer,
-    jni::{JNIEnv, JavaVM, objects::GlobalRef, sys::jint},
+    jni::{
+        JNIEnv, JavaVM,
+        objects::{GlobalRef, JValue},
+        sys::jint,
+    },
     ndk::event::{Keycode, MotionAction},
 };
 // `marker::Sized` explicitly: `crate::prelude::*` below also brings in the
@@ -29,6 +33,10 @@ use super::{
 /// `Option` because a `SurfaceView`'s surface does not outlive backgrounding
 /// the way a winit `Window` does -- `surfaceDestroyed`/`surfaceCreated` can
 /// happen any number of times over the life of one `IrisViewPeer`.
+/// How many frames after each `surface_changed` `render()` logs a full
+/// diagnostic line for -- see the log site's own comment.
+const DIAGNOSTIC_FRAMES: u64 = 10;
+
 pub struct AndroidUiState {
     pub root: Option<StrongWidget>,
     pub renderer: Option<AndroidRenderer>,
@@ -62,10 +70,41 @@ pub struct AndroidUiState {
     /// because `dumpsys gfxinfo` cannot see a `SurfaceView`'s own
     /// GPU-drawn frames at all. See `iris_core::FrameReport`'s own doc.
     pub frame_report: FrameReport,
+    /// `DisplayMetrics.density` (`new_peer`'s doc comment): physical pixels
+    /// per dp on this device, read once at view construction and carried
+    /// on `UiRenderState::density` (`render.set_density`, `new_peer`) from
+    /// then on -- every `Len::dp` in the widget tree resolves against it at
+    /// layout time (`Len::dp`'s field doc, IRIS_TODO.md's
+    /// "density-independent length unit" item, 2026-09-06).
+    ///
+    /// **Everything else in this module is physical pixels, matching the
+    /// real wgpu surface/swapchain resolution** -- window size, touch
+    /// coordinates, insets. That is a correction from an earlier version
+    /// of this comment, which had `window_size`/`surface_changed`'s
+    /// `UiRenderState::resize` call divide by `content_scale` into a
+    /// *logical* coordinate space instead, as a global stopgap for
+    /// RUST.md's P0 box's phone report ("text is far too small"). That
+    /// stopgap fixed the size but not the *sharpness*: dividing to logical
+    /// units meant a `16.0`-sized glyph rasterised at 16 physical px and
+    /// then implicitly upscaled ~3x by the NDC mapping onto the real
+    /// physical framebuffer -- the exact "blurry ... glyphs drawn at
+    /// logical size and stretched by the scale" Iris reported next.
+    /// Resolving `dp` at layout time replaces it: a widget author writes
+    /// `dp(16)` for a size that should look the same physical size on any
+    /// density, and everything downstream (layout, hit-testing, the window
+    /// uniform, and the font size handed to the text shaper) works in the
+    /// display's own physical pixels throughout, so nothing is
+    /// rasterised at one resolution and displayed at another.
+    pub content_scale: f32,
+    /// The last insets `render()` saw -- compared each frame so
+    /// `AndroidAppState::on_insets_changed` fires only when they actually
+    /// change (once at startup for the status bar, again if the device
+    /// rotates), not every frame.
+    last_insets: Insets,
 }
 
 impl AndroidUiState {
-    fn new(shared: Rc<RefCell<Shared>>) -> Self {
+    fn new(shared: Rc<RefCell<Shared>>, content_scale: f32) -> Self {
         Self {
             root: None,
             renderer: None,
@@ -78,6 +117,8 @@ impl AndroidUiState {
             access_adapter: Default::default(),
             access: AccessTree::new(),
             frame_report: FrameReport::new(),
+            content_scale,
+            last_insets: Insets::default(),
         }
     }
 
@@ -120,6 +161,48 @@ pub trait AndroidAppState: HasAndroidUiState {
     /// storing them has no effect on that mechanism.
     #[allow(unused_variables)]
     fn platform_ready(&mut self, rsc: &mut AndroidRsc<Self>, vm: JavaVM, view: GlobalRef) {}
+    /// Called from `render()` whenever `AndroidUiState::insets()` differs
+    /// from what it was last frame -- once at startup for the status bar
+    /// (RUST.md's P0 box: "the status-bar inset is not applied" reported
+    /// the two top buttons sitting under it, because nothing read `.top`
+    /// at all), and again on a rotation or the keyboard opening/closing.
+    /// `insets` is in the same physical-pixel units everything else in the
+    /// tree now uses (`AndroidUiState::content_scale`'s field comment), so
+    /// a widget can add it to a layout size directly -- `dp(...) +
+    /// abs(insets.top)` if the widget wants a density-independent size
+    /// plus the system bar's own (already-physical) height. The default
+    /// does nothing -- most screens have no chrome that sits under a
+    /// system bar.
+    #[allow(unused_variables)]
+    fn on_insets_changed(&mut self, rsc: &mut AndroidRsc<Self>, insets: WindowInsets) {}
+}
+
+/// `insets::Insets` as `f32`, for the widget-facing callback above -- a
+/// distinct type from `insets::Insets` so a caller of `on_insets_changed`
+/// is not coupled to that module's own (`i32`, JNI-shaped) representation.
+/// Both are physical pixels; this used to divide by `content_scale` into a
+/// separate *logical* unit (hence the old name, `LogicalInsets`), back when
+/// the rest of layout was logical too -- see `AndroidUiState::content_scale`'s
+/// field comment for why that stopgap is gone.
+#[derive(Clone, Copy, Default, Debug, PartialEq)]
+pub struct WindowInsets {
+    pub left: f32,
+    pub top: f32,
+    pub right: f32,
+    pub bottom: f32,
+    pub ime_bottom: f32,
+}
+
+impl WindowInsets {
+    fn from_physical(insets: Insets) -> Self {
+        Self {
+            left: insets.left as f32,
+            top: insets.top as f32,
+            right: insets.right as f32,
+            bottom: insets.bottom as f32,
+            ime_bottom: insets.ime_bottom as f32,
+        }
+    }
 }
 
 /// The android-view analogue of `default::DefaultRsc` -- identical in
@@ -266,10 +349,23 @@ impl<State: AndroidAppState> IrisViewPeer<State> {
     /// these in until that is root-caused; removing them loses the exact
     /// evidence a `logcat` capture needs to reproduce the state.
     fn render(&mut self, ctx: &mut CallbackCtx) {
-        let ui_state = self.state.android_state();
+        if self.state.android_state().renderer.is_none() {
-        if ui_state.renderer.is_none() {
             return;
         }
+        // See `AndroidAppState::on_insets_changed`'s doc comment: fires
+        // exactly when insets actually differ from last frame, not every
+        // frame -- most frames this is one `Insets` equality check against
+        // a `Copy` struct. Done before `ui_state` is bound below, since
+        // `on_insets_changed` needs `&mut self.state`/`&mut self.rsc` both.
+        let ui_state = self.state.android_state();
+        let current_insets = ui_state.insets();
+        if current_insets != ui_state.last_insets {
+            let physical = WindowInsets::from_physical(current_insets);
+            self.state.android_state_mut().last_insets = current_insets;
+            self.state.on_insets_changed(&mut self.rsc, physical);
+        }
+
+        let ui_state = self.state.android_state();
         log::debug!(
             "render(): root={:?} widgets={} active={} root_px={:?} out_size={:?}",
             ui_state.root.is_some(),
@@ -294,7 +390,27 @@ impl<State: AndroidAppState> IrisViewPeer<State> {
         let Some(renderer) = &mut ui_state.renderer else {
             return;
         };
-        renderer.update(&mut self.rsc.ui, &mut self.render);
+        let frame_diagnostics = renderer.update(&mut self.rsc.ui, &mut self.render);
+        // First `DIAGNOSTIC_FRAMES` frames after each `surface_changed`
+        // only -- RUST.md's P0 box, "the first input frame" investigation:
+        // the glyph-wipe Iris reported happens on the first tap or scroll
+        // after a fresh surface, so a report from that window is what
+        // would show whether an atlas grow, a masks/move_offsets resize, or
+        // a fresh wgpu error coincided with it. `frame_count()` was just
+        // incremented inside `update()`, so `<=` counts frame 1 through
+        // `DIAGNOSTIC_FRAMES` inclusive.
+        if renderer.frame_count() <= DIAGNOSTIC_FRAMES {
+            log::info!(
+                "iris frame diagnostics: frame={} masks_resized={} moves_resized={} \
+                 atlas_pages_grown_prev={} image_bind_group_creates_prev={} wgpu_errors={}",
+                renderer.frame_count(),
+                frame_diagnostics.masks_resized,
+                frame_diagnostics.moves_resized,
+                frame_diagnostics.atlas_pages_grown_prev,
+                frame_diagnostics.image_bind_group_creates_prev,
+                renderer.wgpu_errors.snapshot().len(),
+            );
+        }
         let submit_to_present = renderer.draw();
         self.state
             .android_state_mut()
@@ -337,6 +453,31 @@ fn show_soft_input<'local>(env: &mut JNIEnv<'local>, view: &View<'local>) {
     imm.show_soft_input(env, view, 0);
 }
 
+/// Replaces the activity's content with a plain, selectable, scrollable
+/// text view holding `report` -- the on-screen half of `surface_changed`'s
+/// renderer-failure path (UI_RULES.md: "a failure is reported where it
+/// happened, and says what to do next," here "copy this and send it").
+/// Goes through an ordinary instance method on the Java side
+/// (`IrisView.showRendererError`) rather than a new `native` method: this
+/// call is Rust reaching *into* Java, the opposite direction from every
+/// `native fn` android-view/`IrisView` declare, and an ordinary virtual
+/// call resolves against `ctx.view`'s real runtime class (`IrisView`) the
+/// same way any other JNI method call here does. Silently does nothing on
+/// any JNI failure -- there is no more-fallback screen to fall back to,
+/// and the `log::error!` in `surface_changed` already reached logcat
+/// first.
+fn show_renderer_error<'local>(env: &mut JNIEnv<'local>, view: &View<'local>, report: &str) {
+    let Ok(message) = env.new_string(report) else {
+        return;
+    };
+    let _ = env.call_method(
+        &view.0,
+        "showRendererError",
+        "(Ljava/lang/String;)V",
+        &[JValue::Object(message.as_ref())],
+    );
+}
+
 impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
     fn on_key_down<'local>(
         &mut self,
@@ -379,6 +520,8 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
     ) -> bool {
         self.drain_tasks();
         let action = event.action_masked(&mut ctx.env);
+        // Device (physical) pixels, same space layout now uses throughout
+        // -- see `AndroidUiState::content_scale`'s field comment.
         let x = event.x(&mut ctx.env);
         let y = event.y(&mut ctx.env);
         let ui_state = self.state.android_state_mut();
@@ -431,7 +574,6 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
         height: i32,
     ) {
         self.drain_tasks();
-        let window = holder.surface(&mut ctx.env).to_native_window(&mut ctx.env);
         // The layout engine's own notion of the canvas size is separate
         // from the wgpu surface's -- winit's backend sets it from
         // `WindowEvent::Resized`, and there is no equivalent automatic
@@ -440,13 +582,101 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
         // nothing but the clear colour: the widget tree laid out against
         // whatever size `UiRenderState::new` starts at instead of the
         // surface's real one.
-        self.render.resize((width as u32, height as u32));
+        //
-        // Drop the old renderer (and the surface it owns) before building
+        // **Physical pixels, matching `AndroidRenderer`'s own
-        // one from the new window -- see `AndroidRenderer`'s doc comment.
+        // `size()`/`resize()`/`new()`** -- `AndroidUiState::content_scale`'s
+        // field comment. This call sets `UiRenderState::output_size`, which
+        // every `rel`/`rest` length resolves against and every `abs`
+        // pixel-region compares to directly; a `dp(56)` height now folds
+        // in the density at `Len::apply_rest` time instead of this call
+        // dividing the whole window into a separate logical space, which
+        // is what used to make every `abs`-unit size (a fixed `.height(56)`
+        // in particular) mean something different from a `rest`-based one.
+        self.render.resize((width as f32, height as f32));
+
+        // **Reuse the existing renderer (device, atlas, buffers, bind
+        // groups) when one is already live -- only reconfigure the
+        // surface.** `surfaceChanged` fires on *every* size or format
+        // change, not only on a genuinely new `Surface`/window: showing
+        // the IME under `adjustResize` resizes the same `SurfaceView` and
+        // is reported through this exact callback. Rebuilding the whole
+        // `AndroidRenderer` here used to mean a fresh `UiRenderNode::new`
+        // -- a brand-new, empty glyph atlas and fresh GPU buffers -- while
+        // `iris_core`'s CPU-side glyph cache (`primitive/text.rs`) kept the
+        // atlas coordinates it had already handed out against the *old*
+        // atlas. Every glyph then drew from a UV rectangle that pointed
+        // into a texture that had just been recreated empty, so text
+        // vanished on the first keyboard open while rects (which never go
+        // through the atlas) kept drawing -- exactly the "rectangles stay,
+        // glyphs disappear" Iris reported. Confirmed by reading this path
+        // end to end (no fresh-atlas rebuild anywhere in `resize()` below,
+        // only in `AndroidRenderer::new`) before changing anything, per
+        // AGENTS.md's "verify before finishing".
+        //
+        // `AndroidRenderer::resize` only reconfigures the wgpu surface and
+        // rewrites the window uniform -- device, atlas, buffers and bind
+        // groups are untouched, so the glyph cache's coordinates stay
+        // valid. A genuinely new surface (after `surface_destroyed`, e.g.
+        // backgrounding) still goes through `AndroidRenderer::new` below,
+        // since `renderer` is `None` in that case.
+        let already_live = self.state.android_state().renderer.is_some();
+        if already_live {
             let ui_state = self.state.android_state_mut();
-        ui_state.renderer = None;
+            ui_state
-        ui_state.renderer = Some(AndroidRenderer::new(window, width as u32, height as u32));
+                .renderer
+                .as_mut()
+                .expect("checked Some above")
+                .resize(width as u32, height as u32);
             self.render(ctx);
+            return;
+        }
+
+        let window = holder.surface(&mut ctx.env).to_native_window(&mut ctx.env);
+        // `AndroidRenderer::new` used to panic here through wgpu's own
+        // default uncaptured-error handler on a bind-group-layout
+        // validation failure -- exactly what aborted the P0 bench APK on
+        // Iris's phone with the message truncated to "wgpu error:
+        // Validation Error" and nothing else recoverable from the crash
+        // report (RUST.md's P0 box, "iris bench crash on the phone,
+        // 2026-09-06"). It now returns the full diagnostic instead; this is
+        // the one place in the app that can turn it into something a
+        // person can read, since `ctx.view`/`ctx.env` (needed to reach the
+        // Java side) are only in scope inside a `ViewPeer` callback.
+        //
+        // `content_scale` reaches `AndroidRenderer` only for the
+        // Diagnostics page's report text now -- window size and the
+        // shader's window uniform are physical pixels throughout (see the
+        // `resize` call above), not divided by it.
+        let content_scale = self.state.android_state().content_scale;
+        match AndroidRenderer::new(window, width as u32, height as u32, content_scale) {
+            Ok(renderer) => {
+                self.state.android_state_mut().renderer = Some(renderer);
+                self.render(ctx);
+            }
+            Err(report) => {
+                // One line for logcat (UI_RULES.md: "the full text for
+                // whoever can read the log" lives here), the multi-line
+                // original on screen -- `show_renderer_error` below.
+                log::error!("iris renderer init failed: {}", report.replace('\n', " | "));
+                // Deferred, not called directly: `Activity::setContentView`
+                // tears the old view hierarchy down synchronously, which
+                // fires `IrisView`'s own `onFocusChanged` before
+                // `setContentView` returns -- straight back into this same
+                // `IrisViewPeer` through `on_focus_changed` while
+                // `with_peer` (android-view's dispatch, `view.rs` upstream)
+                // still holds this peer's `RefCell` borrow for the
+                // `surface_changed` call in progress. Found by inducing a
+                // validation error and hitting `RefCell already borrowed`
+                // at exactly that reentrant call (RUST.md's P0 box).
+                // `push_dynamic_deferred_callback` runs after `with_peer`
+                // drops the borrow, which is what every other callback in
+                // this file that reaches into Java already relies on
+                // (`raise_if_enabled`, above).
+                ctx.push_dynamic_deferred_callback(move |env, view| {
+                    show_renderer_error(env, view, &report);
+                });
+            }
+        }
     }
 
     fn surface_destroyed<'local>(
@@ -557,10 +787,19 @@ impl<State: AndroidAppState> AccessibilityNodeProvider for IrisViewPeer<State> {
 /// `register_view_class`, which wants a plain function pointer) -- see
 /// `iris/android-app/src/lib.rs`.
 pub fn new_peer<'local, State: AndroidAppState>(
-    env: JNIEnv<'local>,
+    mut env: JNIEnv<'local>,
     view: View<'local>,
-    _context: Context<'local>,
+    context: Context<'local>,
 ) -> android_view::jni::sys::jlong {
+    // `DisplayMetrics.density` -- physical pixels per dp on this device.
+    // Read once here, at the one point in this file already handed a
+    // `Context`, and carried on `AndroidUiState` from then on (see
+    // `content_scale`'s field comment for what depends on it).
+    let content_scale = context
+        .resources(&mut env)
+        .display_metrics(&mut env)
+        .density(&mut env);
+    log::info!("iris: new_peer content_scale={content_scale}");
     let vm = env.get_java_vm().unwrap();
     let global_view = env.new_global_ref(&view.0).unwrap();
     let redraw: Arc<dyn RequestRedraw> = Arc::new(AndroidRedrawHandle::new(vm, global_view));
@@ -572,15 +811,22 @@ pub fn new_peer<'local, State: AndroidAppState>(
         state: Default::default(),
         _state: PhantomData,
     };
+    // See `TextData::density`'s field doc for why this is set alongside
+    // `render.set_density` below rather than read from there.
+    rsc.ui.text.density = content_scale;
     let shared = Rc::new(RefCell::new(Shared::default()));
-    let ui_state = AndroidUiState::new(shared.clone());
+    let ui_state = AndroidUiState::new(shared.clone(), content_scale);
     let mut state = State::new(ui_state, &mut rsc);
     let platform_vm = env.get_java_vm().unwrap();
     let platform_view = env.new_global_ref(&view.0).unwrap();
     state.platform_ready(&mut rsc, platform_vm, platform_view);
+    let mut render = UiRenderState::new();
+    // Every `Len::dp` in the tree resolves against this from now on -- see
+    // `UiRenderState::density`'s field doc and `Len::dp`'s.
+    render.set_density(content_scale);
     let peer = IrisViewPeer {
         rsc,
-        render: UiRenderState::new(),
+        render,
         state,
         task_recv,
     };

iris/src/default/input.rs

@@ -11,10 +11,15 @@ pub struct Input {
 }
 
 impl Input {
-    pub fn event(&mut self, event: &WindowEvent) -> bool {
+    /// `scale_factor` converts winit's physical-pixel event coordinates
+    /// into the same logical units `UiRenderNode`'s window uniform now uses
+    /// (`default::render::UiRenderer::new`'s doc comment) -- without it,
+    /// a cursor position and the widget tree it's tested against would be
+    /// in two different units on any monitor whose scale factor isn't 1.0.
+    pub fn event(&mut self, event: &WindowEvent, scale_factor: f32) -> bool {
         match event {
             WindowEvent::CursorMoved { position, .. } => {
-                self.cursor.pos = Vec2::new(position.x as f32, position.y as f32);
+                self.cursor.pos = Vec2::new(position.x as f32, position.y as f32) / scale_factor;
                 self.cursor.exists = true;
             }
             WindowEvent::MouseInput { state, button, .. } => {
@@ -30,7 +35,9 @@ impl Input {
             WindowEvent::MouseWheel { delta, .. } => {
                 let mut delta = match *delta {
                     MouseScrollDelta::LineDelta(x, y) => Vec2::new(x, y),
-                    MouseScrollDelta::PixelDelta(pos) => Vec2::new(pos.x as f32, pos.y as f32),
+                    MouseScrollDelta::PixelDelta(pos) => {
+                        Vec2::new(pos.x as f32, pos.y as f32) / scale_factor
+                    }
                 };
                 if delta.x == 0.0 && self.modifiers.shift {
                     delta.x = delta.y;
@@ -68,8 +75,13 @@ impl Input {
 
 impl DefaultUiState {
     pub fn window_size(&self) -> Vec2 {
-        let size = self.renderer.window().inner_size();
+        let window = self.renderer.window();
-        (size.width, size.height).into()
+        let size = window.inner_size();
+        let scale_factor = window.scale_factor() as f32;
+        Vec2::new(
+            size.width as f32 / scale_factor,
+            size.height as f32 / scale_factor,
+        )
     }
 
     pub fn cursor_state(&self) -> &CursorState {

iris/src/default/mod.rs

@@ -246,7 +246,8 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
         ui_state
             .access_adapter
             .process_event(&ui_state.window, &event);
-        let input_changed = ui_state.input.event(&event);
+        let scale_factor = ui_state.renderer.window().scale_factor() as f32;
+        let input_changed = ui_state.input.event(&event, scale_factor);
         let cursor_state = ui_state.cursor_state().clone();
         let old = ui_state.focus;
         if cursor_state.buttons.left.is_start() {

iris/src/default/render.rs

@@ -1,5 +1,5 @@
 use crate::task::RequestRedraw;
-use iris_core::{UiData, UiRenderNode, UiRenderState};
+use iris_core::{UiData, UiRenderNode, UiRenderState, util::Vec2};
 use pollster::FutureExt;
 use std::sync::Arc;
 use wgpu::*;
@@ -66,7 +66,13 @@ impl UiRenderer {
         self.config.width = size.width;
         self.config.height = size.height;
         self.surface.configure(&self.device, &self.config);
-        self.ui.resize((size.width, size.height), &self.queue);
+        // Logical, matching `new`'s own seed -- see the comment there.
+        let scale_factor = self.window.scale_factor() as f32;
+        let logical = Vec2::new(
+            size.width as f32 / scale_factor,
+            size.height as f32 / scale_factor,
+        );
+        self.ui.resize(logical, &self.queue);
     }
 
     fn create_encoder(device: &Device) -> CommandEncoder {
@@ -141,7 +147,28 @@ impl UiRenderer {
 
         let encoder = Self::create_encoder(&device);
 
-        let ui = UiRenderNode::new(&device, &queue, &config);
+        // Unlike the Android backend, the desktop backend has no on-screen
+        // fallback to show a diagnostic through, so a renderer-creation
+        // failure still panics here -- but now with wgpu's full "Caused
+        // by:" chain as the message, since `UiRenderNode::new` returns it
+        // rather than letting wgpu's own default handler panic first (see
+        // that function's doc comment).
+        // Logical size (physical / `scale_factor`), matching what the
+        // Android backend now reports too (`android::render::
+        // AndroidRenderer::new`, `content_scale`) -- the swapchain still
+        // configures at the real physical resolution above; only the
+        // window uniform layout/hit-testing agree on is scaled. Without
+        // this a window on any monitor whose scale factor isn't 1.0 would
+        // have the identical "everything too small" bug RUST.md's P0 box
+        // found on Iris's phone, just never noticed here because this
+        // crate's own dev monitors happen to run at 1.0.
+        let scale_factor = window.scale_factor() as f32;
+        let logical_size = Vec2::new(
+            size.width as f32 / scale_factor,
+            size.height as f32 / scale_factor,
+        );
+        let ui = UiRenderNode::new(&device, &queue, &config, logical_size)
+            .expect("Could not create iris render node!");
 
         Self {
             surface,

iris/src/sense.rs

@@ -1,5 +1,6 @@
 use crate::prelude::*;
 use std::{
+    collections::VecDeque,
     ops::{BitOr, Deref, DerefMut},
     rc::Rc,
     time::{Duration, Instant},
@@ -491,7 +492,25 @@ impl DragArbiter {
                 } else if dy.abs() > DRAG_SLOP && dy.abs() >= dx.abs() {
                     self.state = ArbiterState::Panning;
                     self.last = pos;
-                    DragOutcome::Pan(dy)
+                    // `dy` here is the *whole* drag since `press_start`,
+                    // not since the last frame -- nothing panned while
+                    // `Undecided` was withholding the slop, so applying it
+                    // in full on this one frame is a visible jump the
+                    // instant `DRAG_SLOP` is crossed (IRIS_TODO.md's
+                    // "scrolling down sometimes jitters the text," root-
+                    // caused by tracing `List`'s per-frame offset against
+                    // a synthetic monotonic drag: the offset held flat for
+                    // every `Undecided` frame, then stepped by several
+                    // frames' worth of motion at once on the frame slop
+                    // was crossed, before resuming ordinary per-frame
+                    // deltas). Only the excess past the slop threshold is
+                    // real, undecided motion the reader hasn't seen
+                    // reflected yet -- so only that excess is applied now,
+                    // the same way Android's own touch handling consumes
+                    // `ViewConfiguration.getScaledTouchSlop()` once from
+                    // the first scroll past it rather than replaying the
+                    // whole pre-threshold drag in one step.
+                    DragOutcome::Pan(dy - DRAG_SLOP.copysign(dy))
                 } else if now.duration_since(self.origin_at) >= LONG_PRESS
                     && dx.abs() <= DRAG_SLOP
                     && dy.abs() <= DRAG_SLOP
@@ -510,6 +529,390 @@ impl DragArbiter {
     pub fn release(&mut self) {
         self.state = ArbiterState::Idle;
     }
+
+    /// Whether the arbiter's current gesture (if any) has committed to
+    /// panning -- what a caller checks at release time to decide whether
+    /// to hand the tracked velocity to [`crate::widget::List::fling`], per
+    /// IRIS_TODO.md's "swiping has no momentum": a fling must only follow
+    /// a pan, never a text selection that happened to end with the finger
+    /// still moving.
+    pub fn is_panning(&self) -> bool {
+        matches!(self.state, ArbiterState::Panning)
+    }
+}
+
+/// How far back a [`VelocityTracker`] looks when estimating a fling's
+/// initial speed -- Android's own `VelocityTracker` defaults to a similar
+/// short window so a gesture's last flick dominates over its slower start.
+const VELOCITY_WINDOW: Duration = Duration::from_millis(100);
+
+/// Tracks a drag's speed along one axis from its last ~100ms of motion, so
+/// a release can be handed a realistic initial velocity for
+/// [`AndroidFlingSpline`]/[`FlingCalculator`] rather than a single frame's
+/// noisy last delta. Fed one timestamped pan delta per frame
+/// (`add_sample`, the same `dy`/`-dy` quantity `DragArbiter::update`'s
+/// `Pan` outcome already carries) and answers `velocity()` in units per
+/// second, matching whatever unit the deltas were in.
+#[derive(Default)]
+pub struct VelocityTracker {
+    /// `(when, delta)` pairs, oldest first, trimmed to `VELOCITY_WINDOW`
+    /// on every `add_sample` -- so this never grows past however many
+    /// frames land in that window.
+    samples: VecDeque<(Instant, f32)>,
+}
+
+impl VelocityTracker {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Forget everything -- called on a fresh press, so a new gesture's
+    /// velocity is never contaminated by the tail of the previous one.
+    pub fn reset(&mut self) {
+        self.samples.clear();
+    }
+
+    /// Record one frame's motion. `delta` is this frame's movement since
+    /// the last sample, not a cumulative position.
+    pub fn add_sample(&mut self, delta: f32, at: Instant) {
+        self.samples.push_back((at, delta));
+        while let Some(&(when, _)) = self.samples.front() {
+            if at.duration_since(when) > VELOCITY_WINDOW {
+                self.samples.pop_front();
+            } else {
+                break;
+            }
+        }
+    }
+
+    /// The estimated speed, in units-per-second, over whatever samples
+    /// currently fall inside the tracking window: total motion divided by
+    /// the elapsed time between the oldest and newest sample still held.
+    /// `0.0` with fewer than two samples (no time span to divide by).
+    pub fn velocity(&self) -> f32 {
+        if self.samples.len() < 2 {
+            return 0.0;
+        }
+        let total: f32 = self.samples.iter().map(|&(_, d)| d).sum();
+        let span = self
+            .samples
+            .back()
+            .unwrap()
+            .0
+            .duration_since(self.samples.front().unwrap().0)
+            .as_secs_f32();
+        if span <= 0.0 { 0.0 } else { total / span }
+    }
+}
+
+/// Android's fling deceleration curve, ported from AOSP's
+/// `android.widget.OverScroller.SplineOverScroller` (the same curve
+/// Compose's `androidx.compose.ui.gestures.AndroidFlingSpline` and
+/// `androidx.compose.foundation.gestures.FlingCalculator` reuse) so a
+/// fling here travels the same distance a Compose `LazyColumn`'s own
+/// `ScrollableDefaults.flingBehavior()` would for the same initial
+/// velocity -- RUST.md's "Benchmark v2" box asked the two apps' fling
+/// phase to be comparable, and IRIS_TODO.md's "swiping has no momentum"
+/// asked for the same physics a reader's muscle memory already expects
+/// from every other Android scroll view.
+///
+/// The curve is a cubic-Bezier-derived spline sampled into two lookup
+/// tables at start-up (`SPLINE`, built once via [`std::sync::OnceLock`]):
+/// `SPLINE_POSITION[i]`/`SPLINE_TIME[i]` give the fraction of total
+/// distance/time elapsed at the `i`th of 100 even steps along the curve's
+/// own parameter. A lookup at an arbitrary time fraction interpolates
+/// between the two bracketing samples.
+mod android_fling_spline {
+    use std::sync::OnceLock;
+
+    const NB_SAMPLES: usize = 100;
+    /// Where the two cubic tension lines cross (AOSP's own constant name
+    /// and value, `SplineOverScroller.INFLEXION`).
+    pub(super) const INFLEXION: f32 = 0.35;
+    const START_TENSION: f32 = 0.5;
+    const END_TENSION: f32 = 1.0;
+    const P1: f32 = START_TENSION * INFLEXION;
+    const P2: f32 = 1.0 - END_TENSION * (1.0 - INFLEXION);
+
+    pub(super) struct Spline {
+        position: [f32; NB_SAMPLES + 1],
+        time: [f32; NB_SAMPLES + 1],
+    }
+
+    fn build() -> Spline {
+        let mut position = [0.0f32; NB_SAMPLES + 1];
+        let mut time = [0.0f32; NB_SAMPLES + 1];
+        let (mut x_min, mut y_min) = (0.0f32, 0.0f32);
+        for i in 0..NB_SAMPLES {
+            let alpha = i as f32 / NB_SAMPLES as f32;
+
+            let mut x_max = 1.0f32;
+            let (mut x, mut coef);
+            loop {
+                x = x_min + (x_max - x_min) / 2.0;
+                coef = 3.0 * x * (1.0 - x);
+                let tx = coef * ((1.0 - x) * START_TENSION + x * END_TENSION) + x * x * x;
+                if (tx - alpha).abs() < 1e-5 {
+                    break;
+                }
+                if tx > alpha {
+                    x_max = x;
+                } else {
+                    x_min = x;
+                }
+            }
+            position[i] = coef * ((1.0 - x) * P1 + x * P2) + x * x * x;
+
+            let mut y_max = 1.0f32;
+            let (mut y, mut coef_y);
+            loop {
+                y = y_min + (y_max - y_min) / 2.0;
+                coef_y = 3.0 * y * (1.0 - y);
+                let dy = coef_y * ((1.0 - y) * START_TENSION + y * END_TENSION) + y * y * y;
+                if (dy - alpha).abs() < 1e-5 {
+                    break;
+                }
+                if dy > alpha {
+                    y_max = y;
+                } else {
+                    y_min = y;
+                }
+            }
+            time[i] = coef_y * ((1.0 - y) * P1 + y * P2) + y * y * y;
+        }
+        position[NB_SAMPLES] = 1.0;
+        time[NB_SAMPLES] = 1.0;
+        Spline { position, time }
+    }
+
+    static SPLINE: OnceLock<Spline> = OnceLock::new();
+
+    /// The fraction of total distance covered at `time_fraction` (0..=1
+    /// of the fling's total duration). Finds the bracketing samples in
+    /// `SPLINE_TIME` and interpolates linearly between their matching
+    /// `SPLINE_POSITION` entries, exactly as AOSP's `SplineOverScroller
+    /// .flingPosition` does.
+    pub(super) fn distance_fraction(time_fraction: f32) -> f32 {
+        let spline = SPLINE.get_or_init(build);
+        let t = time_fraction.clamp(0.0, 1.0);
+        let index = ((t * NB_SAMPLES as f32) as usize).min(NB_SAMPLES - 1);
+        let t_inf = spline.time[index];
+        let t_sup = spline.time[index + 1];
+        let d_inf = spline.position[index];
+        let d_sup = spline.position[index + 1];
+        let span = t_sup - t_inf;
+        if span <= 0.0 {
+            d_inf
+        } else {
+            d_inf + (d_sup - d_inf) * (t - t_inf) / span
+        }
+    }
+}
+
+/// AOSP `SplineOverScroller`'s two other physical constants: the default
+/// `ViewConfiguration.getScrollFriction()` and the deceleration rate a
+/// friction of `0.84` per frame at 60Hz corresponds to
+/// (`ln(0.78)/ln(0.9)`, `SplineOverScroller.DECELERATION_RATE`).
+const FLING_FRICTION: f32 = 0.015;
+fn deceleration_rate() -> f32 {
+    (0.78f32.ln()) / (0.9f32.ln())
+}
+const GRAVITY_EARTH: f32 = 9.80665;
+
+/// Turns an initial fling velocity into a total travel distance and
+/// duration, following AOSP `SplineOverScroller`'s own closed-form
+/// formulas (`getSplineFlingDistance`/the duration half of `fling()`) --
+/// ported the same way Compose's `FlingCalculator` is, including its
+/// `density`-dependent physical coefficient (`computeDeceleration`,
+/// `GravityEarth * 39.37 * density * 160 * friction`). Density and
+/// velocity/distance units cancel algebraically as long as velocity and
+/// the returned distance share one pixel space (physical or logical) --
+/// [`crate::widget::List::fling`] relies on exactly that cancellation to
+/// avoid needing a display density of its own, since iris's `List`
+/// already works in logical (density-independent) pixels throughout.
+pub struct FlingCalculator {
+    physical_coefficient: f32,
+}
+
+impl FlingCalculator {
+    pub fn new(density: f32) -> Self {
+        Self {
+            physical_coefficient: GRAVITY_EARTH * 39.37 * density * 160.0 * FLING_FRICTION,
+        }
+    }
+
+    fn deceleration_for(&self, velocity: f32) -> f32 {
+        (android_fling_spline::INFLEXION * velocity.abs()
+            / (FLING_FRICTION * self.physical_coefficient))
+            .ln()
+    }
+
+    /// Total signed distance the fling travels before settling, in the
+    /// same pixel units `velocity` was given in.
+    pub fn distance(&self, velocity: f32) -> f32 {
+        if velocity == 0.0 {
+            return 0.0;
+        }
+        let l = self.deceleration_for(velocity);
+        let rate = deceleration_rate();
+        let magnitude =
+            FLING_FRICTION * self.physical_coefficient * (rate / (rate - 1.0) * l).exp();
+        magnitude.copysign(velocity)
+    }
+
+    /// How long the fling takes to settle.
+    pub fn duration(&self, velocity: f32) -> Duration {
+        if velocity == 0.0 {
+            return Duration::ZERO;
+        }
+        let l = self.deceleration_for(velocity);
+        let rate = deceleration_rate();
+        Duration::from_secs_f32((l / (rate - 1.0)).exp())
+    }
+
+    /// The signed distance covered by `elapsed` into a fling of this
+    /// `velocity` that started at `t0` -- what a per-frame ticker
+    /// (`List::tick_fling`) calls to find how far to have scrolled by now.
+    /// Clamped to the full `distance()` once `elapsed` reaches
+    /// `duration()`, so a caller need not special-case "past the end."
+    pub fn position_at(&self, velocity: f32, elapsed: Duration) -> f32 {
+        let duration = self.duration(velocity);
+        if duration.is_zero() {
+            return 0.0;
+        }
+        let fraction = (elapsed.as_secs_f32() / duration.as_secs_f32()).min(1.0);
+        self.distance(velocity) * android_fling_spline::distance_fraction(fraction)
+    }
+}
+
+#[cfg(test)]
+mod velocity_tracker_tests {
+    use super::*;
+    use std::sync::LazyLock;
+
+    // A single fixed base rather than a fresh `Instant::now()` per call --
+    // computing it once per test keeps every sample's spacing exact
+    // instead of at the mercy of however long the test itself takes to
+    // run between calls, the same reasoning `drag_arbiter_tests::t` uses.
+    static BASE: LazyLock<Instant> = LazyLock::new(Instant::now);
+
+    fn t(ms: u64) -> Instant {
+        *BASE + Duration::from_millis(ms)
+    }
+
+    #[test]
+    fn fewer_than_two_samples_reports_zero() {
+        let mut v = VelocityTracker::new();
+        assert_eq!(v.velocity(), 0.0);
+        v.add_sample(10.0, t(0));
+        assert_eq!(v.velocity(), 0.0);
+    }
+
+    #[test]
+    fn a_steady_drag_reports_its_own_speed() {
+        // 5px every 10ms, 11 samples spanning 100ms, sums to 55px over
+        // 0.1s -- 550px/s by this tracker's own "sum of deltas over the
+        // span between the oldest and newest held sample" definition.
+        let mut v = VelocityTracker::new();
+        for i in 0..=10 {
+            v.add_sample(5.0, t(i * 10));
+        }
+        assert!((v.velocity() - 550.0).abs() < 1.0, "got {}", v.velocity());
+    }
+
+    #[test]
+    fn only_the_last_100ms_of_samples_count() {
+        // An old, fast burst well outside the window followed by a slow,
+        // steady drag should report the recent speed, not the average of
+        // both -- otherwise a flick that trails off would still fling at
+        // its earlier, faster speed. The burst sits 110ms before the last
+        // sample, just past the 100ms window, so it is evicted.
+        let mut v = VelocityTracker::new();
+        v.add_sample(1000.0, t(0)); // will be 110ms old by the last sample
+        for i in 1..=11 {
+            v.add_sample(1.0, t(i * 10)); // 1px/10ms = 100px/s
+        }
+        assert!(
+            (v.velocity() - 110.0).abs() < 5.0,
+            "old burst leaked into the window: got {}",
+            v.velocity()
+        );
+    }
+
+    #[test]
+    fn reset_forgets_prior_samples() {
+        let mut v = VelocityTracker::new();
+        v.add_sample(500.0, t(0));
+        v.add_sample(500.0, t(10));
+        assert!(v.velocity() != 0.0);
+        v.reset();
+        assert_eq!(v.velocity(), 0.0);
+    }
+}
+
+#[cfg(test)]
+mod fling_calculator_tests {
+    use super::*;
+
+    #[test]
+    fn zero_velocity_flings_nowhere() {
+        let calc = FlingCalculator::new(1.0);
+        assert_eq!(calc.distance(0.0), 0.0);
+        assert_eq!(calc.duration(0.0), Duration::ZERO);
+    }
+
+    #[test]
+    fn distance_grows_with_velocity_and_keeps_its_sign() {
+        let calc = FlingCalculator::new(2.75); // a typical phone's density
+        let d_slow = calc.distance(2000.0);
+        let d_fast = calc.distance(12000.0);
+        assert!(d_slow > 0.0);
+        assert!(d_fast > d_slow);
+        assert_eq!(calc.distance(-12000.0), -d_fast);
+    }
+
+    /// Summing the spline's own per-frame position deltas across the
+    /// whole fling has to land within 1% of the closed-form `distance()`
+    /// -- this is the guarantee that `List::tick_fling`'s per-frame reads
+    /// of `position_at` actually add up to the total the fling promised,
+    /// not merely that the two formulas look plausible independently.
+    #[test]
+    fn integrating_position_at_matches_the_closed_form_distance() {
+        let calc = FlingCalculator::new(1.0);
+        for velocity in [1500.0f32, 5000.0, 12000.0, -12000.0] {
+            let total = calc.distance(velocity);
+            let duration = calc.duration(velocity);
+            let final_position = calc.position_at(velocity, duration);
+            let err = (final_position - total).abs() / total.abs();
+            assert!(
+                err < 0.01,
+                "velocity {velocity}: position_at(duration)={final_position} vs distance()={total}, err={err}"
+            );
+        }
+    }
+
+    #[test]
+    fn position_at_is_monotonic_and_clamped_past_the_end() {
+        let calc = FlingCalculator::new(1.0);
+        let velocity = 12000.0f32;
+        let duration = calc.duration(velocity);
+        let total = calc.distance(velocity);
+        let mut last = 0.0;
+        let mut t = Duration::ZERO;
+        while t < duration {
+            let p = calc.position_at(velocity, t);
+            assert!(p >= last - 0.01, "position went backwards at {t:?}");
+            last = p;
+            t += Duration::from_millis(16);
+        }
+        // Well past the end, it stays pinned at the total -- a caller
+        // must be able to ask "where would this fling be" without first
+        // checking whether it has already settled.
+        assert_eq!(
+            calc.position_at(velocity, duration + Duration::from_secs(5)),
+            total
+        );
+    }
 }
 
 #[cfg(test)]
@@ -534,9 +937,13 @@ mod drag_arbiter_tests {
     fn a_vertical_drag_pans_immediately() {
         let mut a = DragArbiter::new();
         a.press_start(Vec2::new(0.0, 0.0), t(0), false);
+        // The transition frame applies only the motion past `DRAG_SLOP`
+        // (20 - 8 = 12), not the full 20px since `press_start` -- see the
+        // `Pan` arm's own comment for why replaying the whole withheld
+        // drag in one step is the scroll-jitter bug this guards against.
         assert_eq!(
             a.update(Vec2::new(0.0, 20.0), t(10)),
-            DragOutcome::Pan(20.0)
+            DragOutcome::Pan(12.0)
         );
         // Subsequent frames keep panning, by the delta since last frame.
         assert_eq!(
@@ -545,6 +952,22 @@ mod drag_arbiter_tests {
         );
     }
 
+    /// Direct regression test for the fix: a slow drag that crosses
+    /// `DRAG_SLOP` by only a fraction of a pixel must not still produce a
+    /// visible jump -- the amount applied on the crossing frame should
+    /// itself shrink toward zero as the crossing gets closer to exactly
+    /// `DRAG_SLOP`, rather than always dumping the whole pre-threshold
+    /// distance at once.
+    #[test]
+    fn crossing_the_slop_by_a_little_pans_by_a_little() {
+        let mut a = DragArbiter::new();
+        a.press_start(Vec2::new(0.0, 0.0), t(0), false);
+        assert_eq!(
+            a.update(Vec2::new(0.0, DRAG_SLOP + 0.5), t(10)),
+            DragOutcome::Pan(0.5)
+        );
+    }
+
     #[test]
     fn a_horizontal_drag_with_nothing_selected_does_not_select() {
         let mut a = DragArbiter::new();
@@ -603,7 +1026,7 @@ mod drag_arbiter_tests {
         a.press_start(Vec2::new(0.0, 0.0), t(0), true);
         assert_eq!(
             a.update(Vec2::new(0.0, 20.0), t(10)),
-            DragOutcome::Pan(20.0)
+            DragOutcome::Pan(12.0)
         );
     }
 
@@ -646,7 +1069,7 @@ mod drag_arbiter_tests {
         a.press_start(Vec2::new(0.0, 700.0), t(0), false);
         assert_eq!(
             a.update(Vec2::new(0.0, 720.0), t(10)),
-            DragOutcome::Pan(20.0)
+            DragOutcome::Pan(12.0)
         );
         assert!(!a.is_idle());
     }

iris/src/widget/list.rs

@@ -102,7 +102,7 @@
 
 use crate::prelude::*;
 use iris_core::util::HashMap;
-use std::collections::VecDeque;
+use std::{collections::VecDeque, sync::Arc, time::Instant};
 
 /// A stable identifier for a loaded row, reused across pages so that a row
 /// already measured and drawn is not treated as new when data is inserted
@@ -213,6 +213,39 @@ pub struct List {
     /// row is evicted (`pop_front`/`pop_back`) so this cannot grow past
     /// however many rows are currently loaded.
     heights: HashMap<RowKey, f32>,
+    /// A fling in progress, or `None` if the list is at rest -- see
+    /// `fling`/`tick_fling`/`is_scrolling`, IRIS_TODO.md's "swiping has no
+    /// momentum."
+    fling: Option<Fling>,
+    /// What `tick_fling` re-arms every frame a fling is still running, so
+    /// the list keeps animating without needing a caller to poll it --
+    /// set once via `set_redraw_handle` by whoever owns the surface this
+    /// list draws into (the same handle `iris::task::Tasks::redraw_handle`
+    /// hands out elsewhere). `None` for a list that never flings
+    /// (headless tests, a caller driving `tick_fling` by hand as
+    /// `bench_client.rs`'s scripted phases do).
+    redraw: Option<Arc<dyn RequestRedraw>>,
+    /// Whether the last `draw` found no more content above the topmost
+    /// visible row (its top edge at or past the viewport's own top, with
+    /// no `prev_slot`) -- what `tick_fling` clamps a fling moving toward
+    /// the start against. Stale (from whatever the last draw found) on a
+    /// list that hasn't drawn yet; `false` by default, matching "assume
+    /// there is more content until a draw proves otherwise."
+    at_start: bool,
+    /// The mirror of `at_start` for the newest end.
+    at_end: bool,
+}
+
+/// One in-flight fling: the physics answer (`FlingCalculator`) plus how
+/// much of its total distance has already been applied to the anchor, so
+/// `tick_fling` only ever moves the list by this frame's *incremental*
+/// delta -- matching every other place in this widget that scrolls by
+/// writing `anchor.offset`.
+struct Fling {
+    calc: FlingCalculator,
+    velocity: f32,
+    started_at: Instant,
+    applied: f32,
 }
 
 impl List {
@@ -226,6 +259,10 @@ impl List {
             snap_end: true,
             viewport_len: 0.0,
             last_viewport_len: 0.0,
+            fling: None,
+            redraw: None,
+            at_start: false,
+            at_end: false,
             pending_tap: None,
             extents: HashMap::default(),
             heights: HashMap::default(),
@@ -317,6 +354,40 @@ impl List {
         self.extents.clear();
     }
 
+    /// Swap the last row's widget for a new one **without moving it**: the
+    /// slot index is unchanged, so an anchor already pointing at this slot
+    /// (in particular `snap_end`'s pinned-to-newest case) stays pinned, and
+    /// an anchor pointing anywhere else -- this row scrolled out of view --
+    /// is untouched, so nothing currently on screen moves. This is what a
+    /// streamed reply needs: the row whose *content* keeps changing after
+    /// it first appears is still the same row by position, even if its
+    /// `RowKey` happens to change too (rare -- only `heights`/`extents` care
+    /// about the key, and both are invalidated here the same way
+    /// `pop_back` already invalidates them for the row it removes).
+    /// `None` if the list is empty. O(1), same as `push_back`/`pop_back`.
+    pub fn replace_back(&mut self, row: ListRow) -> Option<ListRow> {
+        let idx = self.items.len().checked_sub(1)?;
+        let old = std::mem::replace(&mut self.items[idx], row);
+        self.heights.remove(&old.key);
+        self.extents.clear();
+        Some(old)
+    }
+
+    /// Drop every loaded row and reset to the same state `List::new` would
+    /// give -- the fallback path for a change `apply`-style incremental
+    /// callers can't express as a replace-or-append (RUST.md: `group_tool_runs`
+    /// regrouping an earlier row). `more_before`/`more_after` are left
+    /// alone: a full paging reset is a different operation from "the
+    /// content changed," and a caller that wants both calls
+    /// `set_more_before(None)`/`set_more_after(None)` itself.
+    pub fn clear(&mut self) {
+        self.items.clear();
+        self.anchor = None;
+        self.snap_end = true;
+        self.heights.clear();
+        self.extents.clear();
+    }
+
     /// Move the anchor's edge by `amt` pixels. Positive moves later
     /// content into view (mirrors `Scroll::scroll`'s sign convention).
     /// Deliberately unclamped -- see the module doc's "what is not
@@ -327,6 +398,97 @@ impl List {
         }
     }
 
+    /// Give this list a way to ask for another frame on its own, so a
+    /// fling keeps animating without a caller polling it every tick --
+    /// see the `redraw` field's doc. Pass the same handle
+    /// `iris::task::Tasks::redraw_handle` hands a `spawn`ed task; a list
+    /// that never calls this can still `fling`, but has to be driven by a
+    /// caller-owned loop instead (`bench_client.rs`'s scripted phases do
+    /// exactly that, since they need to await settling rather than let it
+    /// run in the background).
+    pub fn set_redraw_handle(&mut self, handle: Arc<dyn RequestRedraw>) {
+        self.redraw = Some(handle);
+    }
+
+    /// Start a fling at `velocity_px_per_s` (this widget's own pixel
+    /// space, same sign convention as `scroll`'s `amt`: positive continues
+    /// moving later content into view). Cancels any fling already in
+    /// progress. A caller with a live touch/press must cancel this on the
+    /// next touch-down (`cancel_fling`) -- `AndroidFlingSpline`'s curve
+    /// has no idea a finger came back down, and Android's own `Scroller`
+    /// relies on the view calling `abortAnimation` for the same reason.
+    ///
+    /// Density cancels out of the underlying spline as long as velocity
+    /// and the distance it produces share one pixel space (see
+    /// `FlingCalculator`'s own doc) -- `List` works entirely in logical
+    /// pixels, so `1.0` here is not a placeholder for "unknown density,"
+    /// it is the correct density for a self-consistent unit system.
+    pub fn fling(&mut self, velocity_px_per_s: f32) {
+        if velocity_px_per_s == 0.0 || self.anchor.is_none() {
+            self.fling = None;
+            return;
+        }
+        self.fling = Some(Fling {
+            calc: FlingCalculator::new(1.0),
+            velocity: velocity_px_per_s,
+            started_at: Instant::now(),
+            applied: 0.0,
+        });
+    }
+
+    /// Whether a fling is currently animating. What a caller's own
+    /// per-frame loop polls to know when to stop driving `tick_fling`
+    /// (`bench_client.rs`'s fling phase) or to decide whether the list is
+    /// "moving on its own" for any other purpose.
+    pub fn is_scrolling(&self) -> bool {
+        self.fling.is_some()
+    }
+
+    /// Cancel any fling in progress with no further movement -- the next
+    /// touch-down's job, per `fling`'s own doc.
+    pub fn cancel_fling(&mut self) {
+        self.fling = None;
+    }
+
+    /// Advance an in-flight fling to `now`, applying this call's share of
+    /// its total travel via `scroll` and re-arming this list's own redraw
+    /// handle (if it has one) for another frame. Returns whether the
+    /// fling is still going after this call -- `false` either because it
+    /// settled on its own spline-decided schedule or because it reached
+    /// `at_start`/`at_end` (the module doc's clamp: a fling must not carry
+    /// the list past content that does not exist, unlike an ordinary
+    /// touch-pan, which this widget already leaves unclamped by design).
+    ///
+    /// Safe to call even with no fling active (a no-op returning `false`),
+    /// so a caller does not need to check `is_scrolling` first.
+    pub fn tick_fling(&mut self, now: Instant) -> bool {
+        let Some(f) = &mut self.fling else {
+            return false;
+        };
+        let elapsed = now.saturating_duration_since(f.started_at);
+        let target = f.calc.position_at(f.velocity, elapsed);
+        let delta = target - f.applied;
+        f.applied = target;
+        let settled_on_schedule = elapsed >= f.calc.duration(f.velocity);
+        let velocity = f.velocity;
+        self.scroll(delta);
+
+        // Clamp: a fling moving toward the start that has already reached
+        // it (or one moving toward the end that has already reached that)
+        // stops rather than continuing to spend its remaining distance on
+        // a part of the list that will never scroll further.
+        let hit_bound = (velocity < 0.0 && self.at_start) || (velocity > 0.0 && self.at_end);
+
+        if settled_on_schedule || hit_bound {
+            self.fling = None;
+            return false;
+        }
+        if let Some(redraw) = &self.redraw {
+            redraw.request_redraw();
+        }
+        true
+    }
+
     /// Snap to the newest content (last item, or the `more_after`
     /// sentinel if set), bottom-aligned to the viewport. O(1).
     pub fn jump_to_end(&mut self) {
@@ -572,9 +734,10 @@ impl List {
         let axis = self.axis;
         let output_len = painter.output_size().axis(axis);
         let container_len = painter.region().axis(axis).len();
+        let density = painter.density();
         let resolve = move |used: Size| -> f32 {
             used.axis(axis)
-                .apply_rest()
+                .apply_rest(density)
                 .within_len(container_len)
                 .to_abs(output_len)
         };
@@ -690,26 +853,33 @@ impl Widget for List {
         };
         let (mut top, mut bottom) = self.place(painter, anchor.slot, placement);
 
-        let mut idx = anchor.slot;
+        let mut idx_top = anchor.slot;
         while top > 0.0 {
-            let Some(prev) = self.prev_slot(idx) else {
+            let Some(prev) = self.prev_slot(idx_top) else {
                 break;
             };
             let (t, _) = self.place(painter, prev, Placement::Bottom(top));
             top = t;
-            idx = prev;
+            idx_top = prev;
         }
 
-        idx = anchor.slot;
+        let mut idx_bottom = anchor.slot;
         while bottom < self.viewport_len {
-            let Some(next) = self.next_slot(idx) else {
+            let Some(next) = self.next_slot(idx_bottom) else {
                 break;
             };
             let (_, b) = self.place(painter, next, Placement::Top(bottom));
             bottom = b;
-            idx = next;
+            idx_bottom = next;
         }
 
+        // What `tick_fling` clamps a fling against -- see `at_start`'s
+        // field doc. `top`/`bottom` are the extreme edges actually placed
+        // this frame, and `prev_slot`/`next_slot` returning `None` is what
+        // "no more content" means everywhere else in this widget.
+        self.at_start = self.prev_slot(idx_top).is_none() && top >= 0.0;
+        self.at_end = self.next_slot(idx_bottom).is_none() && bottom <= self.viewport_len;
+
         self.update_snap_end();
         Size::REST
     }
@@ -1032,4 +1202,258 @@ mod tests {
             assert!(moves <= 12, "n={n}: expected O(visible) moves, got {moves}");
         }
     }
+
+    /// The streamed-reply case (RUST.md's "streaming still costs a full
+    /// rebuild" fix, `transcript-ui::TranscriptScreen::apply`): a delta
+    /// swaps the last row's widget for a taller one, same key, same slot.
+    /// A list flush with its own end (the default, `snap_end`) must stay
+    /// flush -- the row grows *upward* from the pinned bottom edge, not
+    /// the other way around, exactly like an ordinary resize of that same
+    /// row would (`expanding_a_row_holds_the_bottom_edge_when_tap_is_lower`).
+    #[test]
+    fn replacing_the_last_row_stays_pinned_to_the_bottom() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let mut list = List::new(Axis::Y);
+        push_rows(&mut rsc, &mut list, &[0, 1, 2, 3, 4], 20.0);
+        let (list_weak, root) = add_list(&mut rsc, list);
+
+        let mut render = UiRenderState::new();
+        render.resize((100.0, 60.0));
+        render.update(&root, &mut rsc);
+
+        // Row 4 is flush with the viewport's bottom edge before the replace.
+        {
+            let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+            assert!((list_ref.extents[&4].bottom - 60.0).abs() < 0.01);
+        }
+
+        let (_weak, new_row) = fixed_row(&mut rsc, 40.0);
+        let old = rsc
+            .ui
+            .widgets
+            .get_mut(&list_weak)
+            .unwrap()
+            .replace_back(ListRow::new(4, new_row));
+        assert!(
+            old.is_some(),
+            "replace_back should hand back the row it evicted"
+        );
+
+        render.update(&root, &mut rsc);
+
+        let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+        let row4 = list_ref.extents[&4];
+        assert!(
+            (row4.bottom - 60.0).abs() < 0.01,
+            "still pinned to the newest end after the replace: {row4:?}"
+        );
+        assert!(
+            (row4.top - 20.0).abs() < 0.01,
+            "grew upward, from the pinned bottom edge: {row4:?}"
+        );
+    }
+
+    /// The other half of the same fix's contract: replacing a row that is
+    /// *not* on screen must not move anything that is. `replace_back` only
+    /// touches the last slot's own widget and this file's own `heights`/
+    /// `extents` caches for that one key -- nothing about `Anchor` changes
+    /// -- so the already-placed rows above it should come out at the exact
+    /// same boxes on the next frame.
+    #[test]
+    fn replacing_the_last_row_out_of_view_does_not_move_visible_rows() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let mut list = List::new(Axis::Y);
+        push_rows(&mut rsc, &mut list, &[0, 1, 2, 3, 4], 20.0);
+        let (list_weak, root) = add_list(&mut rsc, list);
+
+        let mut render = UiRenderState::new();
+        render.resize((100.0, 60.0));
+        // Settle at the default (bottom) anchor first -- `jump_to_start`
+        // does not touch `snap_end`, and `repair_anchor` only leaves a
+        // freshly-set anchor's offset alone once `viewport_len` has
+        // already matched `last_viewport_len` once, the same reason
+        // `moves_stay_o1_across_list_size` settles before the tick it
+        // actually measures.
+        render.update(&root, &mut rsc);
+        // Scrolled to the oldest content: rows 0,1,2 visible, row 4 is far
+        // below the viewport.
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().jump_to_start();
+        render.update(&root, &mut rsc);
+
+        let (before0, before1, before2) = {
+            let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+            assert!(!list_ref.extents.contains_key(&4));
+            (
+                list_ref.extents[&0],
+                list_ref.extents[&1],
+                list_ref.extents[&2],
+            )
+        };
+
+        let (_weak, new_row) = fixed_row(&mut rsc, 999.0);
+        rsc.ui
+            .widgets
+            .get_mut(&list_weak)
+            .unwrap()
+            .replace_back(ListRow::new(4, new_row));
+
+        render.update(&root, &mut rsc);
+
+        let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+        for (key, before) in [(0u64, before0), (1, before1), (2, before2)] {
+            let after = list_ref.extents[&key];
+            assert_eq!(
+                (after.top, after.bottom),
+                (before.top, before.bottom),
+                "row {key} moved after an off-screen replace"
+            );
+        }
+    }
+
+    /// Enough rows, tall enough, that a fling toward the start has real
+    /// room to travel before `at_start` clamps it -- shared by the fling
+    /// tests below.
+    fn build_flingable_list(rsc: &mut TestRsc) -> (WeakWidget<List>, StrongWidget, UiRenderState) {
+        let mut list = List::new(Axis::Y);
+        push_rows(rsc, &mut list, &(0..200).collect::<Vec<_>>(), 20.0);
+        let (list_weak, root) = add_list(rsc, list);
+        let mut render = UiRenderState::new();
+        render.resize((100.0, 600.0));
+        render.update(&root, rsc);
+        (list_weak, root, render)
+    }
+
+    #[test]
+    fn fling_moves_the_list_and_then_settles() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let (list_weak, root, mut render) = build_flingable_list(&mut rsc);
+
+        // A fling toward the start: negative velocity, matching `scroll`'s
+        // sign convention (`Selection::drag` calls `scroll(-dy)` for a
+        // downward finger motion revealing older content).
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().fling(-8000.0);
+        assert!(rsc.ui.widgets.get(&list_weak).unwrap().is_scrolling());
+
+        let start = Instant::now();
+        let mut last_still_scrolling = true;
+        for step in 0..600 {
+            let now = start + std::time::Duration::from_millis(step * 16);
+            last_still_scrolling = rsc.ui.widgets.get_mut(&list_weak).unwrap().tick_fling(now);
+            render.update(&root, &mut rsc);
+            if !last_still_scrolling {
+                break;
+            }
+        }
+        assert!(
+            !last_still_scrolling,
+            "fling never settled within 600 steps"
+        );
+        assert!(!rsc.ui.widgets.get(&list_weak).unwrap().is_scrolling());
+    }
+
+    #[test]
+    fn fling_distance_is_positive_toward_the_end() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let (list_weak, root, mut render) = build_flingable_list(&mut rsc);
+        // Start scrolled away from the newest end so there is room for an
+        // end-ward fling to actually move.
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().jump_to_start();
+        render.update(&root, &mut rsc);
+        let before = rsc.ui.widgets.get(&list_weak).unwrap().extents[&0];
+
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().fling(8000.0);
+        let start = Instant::now();
+        for step in 0..600 {
+            let now = start + std::time::Duration::from_millis(step * 16);
+            let still = rsc.ui.widgets.get_mut(&list_weak).unwrap().tick_fling(now);
+            render.update(&root, &mut rsc);
+            if !still {
+                break;
+            }
+        }
+        let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+        // Row 0 either scrolled out of the loaded extents (flung well past
+        // it) or moved upward (smaller top) -- either way, real motion
+        // happened toward the end rather than staying put.
+        if let Some(after) = list_ref.extents.get(&0) {
+            assert!(
+                after.top < before.top,
+                "fling toward the end did not move content up"
+            );
+        }
+    }
+
+    #[test]
+    fn cancel_fling_stops_it_with_no_further_movement() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let (list_weak, root, mut render) = build_flingable_list(&mut rsc);
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().fling(-8000.0);
+        let start = Instant::now();
+        rsc.ui
+            .widgets
+            .get_mut(&list_weak)
+            .unwrap()
+            .tick_fling(start + std::time::Duration::from_millis(16));
+        render.update(&root, &mut rsc);
+        assert!(rsc.ui.widgets.get(&list_weak).unwrap().is_scrolling());
+
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().cancel_fling();
+        assert!(!rsc.ui.widgets.get(&list_weak).unwrap().is_scrolling());
+
+        let before = rsc.ui.widgets.get(&list_weak).unwrap().extents[&199];
+        // A tick after cancelling must be a no-op -- this is what a fresh
+        // touch-down relies on to stop a fling in its tracks.
+        let still = rsc
+            .ui
+            .widgets
+            .get_mut(&list_weak)
+            .unwrap()
+            .tick_fling(start + std::time::Duration::from_millis(200));
+        render.update(&root, &mut rsc);
+        assert!(!still);
+        let after = rsc.ui.widgets.get(&list_weak).unwrap().extents[&199];
+        assert_eq!((before.top, before.bottom), (after.top, after.bottom));
+    }
+
+    #[test]
+    fn fling_toward_the_start_stops_at_the_first_row() {
+        let mut rsc = TestRsc {
+            ui: UiData::default(),
+        };
+        let (list_weak, root, mut render) = build_flingable_list(&mut rsc);
+        // An enormous velocity that would travel far past all 200 rows if
+        // unclamped -- this is exactly what IRIS_TODO.md's "way faster...
+        // better for stress testing" fling asks for.
+        rsc.ui.widgets.get_mut(&list_weak).unwrap().fling(-50_000.0);
+        let start = Instant::now();
+        for step in 0..2000 {
+            let now = start + std::time::Duration::from_millis(step * 16);
+            let still = rsc.ui.widgets.get_mut(&list_weak).unwrap().tick_fling(now);
+            render.update(&root, &mut rsc);
+            if !still {
+                break;
+            }
+        }
+        let list_ref = rsc.ui.widgets.get(&list_weak).unwrap();
+        assert!(
+            list_ref.at_start,
+            "fling should have clamped at the first row"
+        );
+        let first = list_ref.extents[&0];
+        assert!(
+            first.top >= -0.5,
+            "clamped fling overshot the first row's top: {}",
+            first.top
+        );
+    }
 }

iris/src/widget/position/align.rs

@@ -17,14 +17,15 @@ impl Widget for Aligned {
         // already-resolved region double-applies that composition and is
         // wrong for any widget nested below the root.
         let used = painter.widget(&self.inner);
+        let density = painter.density();
         let region = match self.align.tuple() {
-            (Some(x), Some(y)) => used.to_uivec2().align(RegionAlign { x, y }),
+            (Some(x), Some(y)) => used.to_uivec2(density).align(RegionAlign { x, y }),
             (Some(x), None) => {
-                let x = used.x.apply_rest().align(x);
+                let x = used.x.apply_rest(density).align(x);
                 UiRegion::new(x, UiSpan::FULL)
             }
             (None, Some(y)) => {
-                let y = used.y.apply_rest().align(y);
+                let y = used.y.apply_rest(density).align(y);
                 UiRegion::new(UiSpan::FULL, y)
             }
             (None, None) => UiRegion::FULL,

iris/src/widget/position/max_size.rs

@@ -9,12 +9,12 @@ pub struct MaxSize {
 impl MaxSize {
     /// Caps a reported length at `max`, comparing in pixels since `Len`'s
     /// rel/abs/rest components are not otherwise comparable.
-    fn clamp(len: Len, max: Option<Len>, output: f32) -> Len {
+    fn clamp(len: Len, max: Option<Len>, output: f32, density: f32) -> Len {
         let Some(max) = max else {
             return len;
         };
-        let len_px = len.apply_rest().to_abs(output);
+        let len_px = len.apply_rest(density).to_abs(output);
-        let max_px = max.apply_rest().to_abs(output);
+        let max_px = max.apply_rest(density).to_abs(output);
         if len_px > max_px { max } else { len }
     }
 
@@ -24,11 +24,11 @@ impl MaxSize {
     /// start, if it does not. Needed so the child is never painted bigger
     /// than the size this widget reports for it -- see the identical
     /// requirement noted on `Sized::draw`.
-    fn clamp_region(offered_px: f32, max: Option<Len>, output: f32) -> UiSpan {
+    fn clamp_region(offered_px: f32, max: Option<Len>, output: f32, density: f32) -> UiSpan {
         let Some(max) = max else {
             return UiSpan::FULL;
         };
-        let max_scalar = max.apply_rest();
+        let max_scalar = max.apply_rest(density);
         let max_px = max_scalar.to_abs(output);
         if offered_px > max_px {
             max_scalar.align(AxisAlign::Neg)
@@ -41,15 +41,16 @@ impl MaxSize {
 impl Widget for MaxSize {
     fn draw(&mut self, painter: &mut Painter) -> Size {
         let output = painter.output_size();
+        let density = painter.density();
         let offered = painter.px_size();
         let region = UiRegion {
-            x: Self::clamp_region(offered.x, self.x, output.x),
+            x: Self::clamp_region(offered.x, self.x, output.x, density),
-            y: Self::clamp_region(offered.y, self.y, output.y),
+            y: Self::clamp_region(offered.y, self.y, output.y, density),
         };
         let used = painter.widget_within(&self.inner, region);
         Size {
-            x: Self::clamp(used.x, self.x, output.x),
+            x: Self::clamp(used.x, self.x, output.x, density),
-            y: Self::clamp(used.y, self.y, output.y),
+            y: Self::clamp(used.y, self.y, output.y, density),
         }
     }
 }

iris/src/widget/position/pad.rs

@@ -7,9 +7,12 @@ pub struct Pad {
 
 impl Widget for Pad {
     fn draw(&mut self, painter: &mut Painter) -> Size {
-        let used = painter.widget_within(&self.inner, self.padding.region());
+        let density = painter.density();
-        let width = self.padding.left + self.padding.right;
+        let used = painter.widget_within(&self.inner, self.padding.region(density));
-        let height = self.padding.top + self.padding.bottom;
+        let width =
+            self.padding.left.apply_rest(density).abs + self.padding.right.apply_rest(density).abs;
+        let height =
+            self.padding.top.apply_rest(density).abs + self.padding.bottom.apply_rest(density).abs;
         Size {
             x: used.x + Len::abs(width),
             y: used.y + Len::abs(height),
@@ -17,23 +20,29 @@ impl Widget for Pad {
     }
 }
 
+/// Each side is a `Len`, not a bare `f32`, so `.pad(dp(10))` resolves
+/// against the display's density the same way any other size does -- see
+/// `Len::dp`'s field doc. `.pad(10)` (a bare number) still works via
+/// `From<T: UiNum>` below, unchanged: it becomes an `abs` (physical-pixel)
+/// `Len`, exactly as a bare number always has meant elsewhere in this
+/// crate.
 pub struct Padding {
-    pub left: f32,
+    pub left: Len,
-    pub right: f32,
+    pub right: Len,
-    pub top: f32,
+    pub top: Len,
-    pub bottom: f32,
+    pub bottom: Len,
 }
 
 impl Padding {
     pub const ZERO: Self = Self {
-        left: 0.0,
+        left: Len::ZERO,
-        right: 0.0,
+        right: Len::ZERO,
-        top: 0.0,
+        top: Len::ZERO,
-        bottom: 0.0,
+        bottom: Len::ZERO,
     };
 
-    pub fn uniform(amt: impl UiNum) -> Self {
+    pub fn uniform(amt: impl Into<Len>) -> Self {
-        let amt = amt.to_f32();
+        let amt = amt.into();
         Self {
             left: amt,
             right: amt,
@@ -41,80 +50,84 @@ impl Padding {
             bottom: amt,
         }
     }
-    pub fn region(&self) -> UiRegion {
+    pub fn region(&self, density: f32) -> UiRegion {
         let mut region = UiRegion::FULL;
-        region.x.start.abs += self.left;
+        region.x.start.abs += self.left.apply_rest(density).abs;
-        region.y.start.abs += self.top;
+        region.y.start.abs += self.top.apply_rest(density).abs;
-        region.x.end.abs -= self.right;
+        region.x.end.abs -= self.right.apply_rest(density).abs;
-        region.y.end.abs -= self.bottom;
+        region.y.end.abs -= self.bottom.apply_rest(density).abs;
         region
     }
-    pub fn x(amt: impl UiNum) -> Self {
+    pub fn x(amt: impl Into<Len>) -> Self {
-        let amt = amt.to_f32();
+        let amt = amt.into();
         Self {
             left: amt,
             right: amt,
-            top: 0.0,
+            top: Len::ZERO,
-            bottom: 0.0,
+            bottom: Len::ZERO,
         }
     }
-    pub fn y(amt: impl UiNum) -> Self {
+    pub fn y(amt: impl Into<Len>) -> Self {
-        let amt = amt.to_f32();
+        let amt = amt.into();
         Self {
-            left: 0.0,
+            left: Len::ZERO,
-            right: 0.0,
+            right: Len::ZERO,
             top: amt,
             bottom: amt,
         }
     }
 
-    pub fn top(amt: impl UiNum) -> Self {
+    pub fn top(amt: impl Into<Len>) -> Self {
         let mut s = Self::ZERO;
-        s.top = amt.to_f32();
+        s.top = amt.into();
         s
     }
 
-    pub fn bottom(amt: impl UiNum) -> Self {
+    pub fn bottom(amt: impl Into<Len>) -> Self {
         let mut s = Self::ZERO;
-        s.bottom = amt.to_f32();
+        s.bottom = amt.into();
         s
     }
 
-    pub fn left(amt: impl UiNum) -> Self {
+    pub fn left(amt: impl Into<Len>) -> Self {
         let mut s = Self::ZERO;
-        s.left = amt.to_f32();
+        s.left = amt.into();
         s
     }
 
-    pub fn right(amt: impl UiNum) -> Self {
+    pub fn right(amt: impl Into<Len>) -> Self {
         let mut s = Self::ZERO;
-        s.right = amt.to_f32();
+        s.right = amt.into();
         s
     }
 
-    pub fn with_top(mut self, amt: impl UiNum) -> Self {
+    pub fn with_top(mut self, amt: impl Into<Len>) -> Self {
-        self.top = amt.to_f32();
+        self.top = amt.into();
         self
     }
 
-    pub fn with_bottom(mut self, amt: impl UiNum) -> Self {
+    pub fn with_bottom(mut self, amt: impl Into<Len>) -> Self {
-        self.bottom = amt.to_f32();
+        self.bottom = amt.into();
         self
     }
 
-    pub fn with_left(mut self, amt: impl UiNum) -> Self {
+    pub fn with_left(mut self, amt: impl Into<Len>) -> Self {
-        self.left = amt.to_f32();
+        self.left = amt.into();
         self
     }
 
-    pub fn with_right(mut self, amt: impl UiNum) -> Self {
+    pub fn with_right(mut self, amt: impl Into<Len>) -> Self {
-        self.right = amt.to_f32();
+        self.right = amt.into();
         self
     }
 }
 
-impl<T: UiNum> From<T> for Padding {
+/// Covers both a bare number (`.pad(8)`, via `Len`'s own `From<N: UiNum>`
+/// blanket -- an `abs`/physical-pixel `Len`) and a `Len` directly
+/// (`.pad(dp(10))`) with the one impl, since `Len: Into<Len>` is the
+/// reflexive case of the same bound.
+impl<T: Into<Len>> From<T> for Padding {
     fn from(amt: T) -> Self {
-        Self::uniform(amt.to_f32())
+        Self::uniform(amt.into())
     }
 }

iris/src/widget/position/scroll.rs

@@ -43,7 +43,7 @@ impl Widget for Scroll {
 
         self.content_len = used
             .axis(axis)
-            .apply_rest()
+            .apply_rest(painter.density())
             .within_len(container_len)
             .to_abs(output_len);
 

iris/src/widget/position/sized.rs

@@ -17,12 +17,13 @@ impl Widget for Sized {
         // learn its size, then moves it into place with a pure
         // translation; that translation is only valid if what got painted
         // is already the reported size, anchored the same way both times.
+        let density = painter.density();
         let mut region = UiRegion::FULL;
         if let Some(x) = self.x {
-            region.x = x.apply_rest().align(AxisAlign::Neg);
+            region.x = x.apply_rest(density).align(AxisAlign::Neg);
         }
         if let Some(y) = self.y {
-            region.y = y.apply_rest().align(AxisAlign::Neg);
+            region.y = y.apply_rest(density).align(AxisAlign::Neg);
         }
         let used = painter.widget_within(&self.inner, region);
         Size {

iris/src/widget/position/span.rs

@@ -4,12 +4,18 @@ use std::marker::PhantomData;
 pub struct Span {
     pub children: Vec<StrongWidget>,
     pub dir: Dir,
-    pub gap: f32,
+    /// A `Len` (not a bare `f32`) so `dp(4)` resolves against the display's
+    /// density the same way any other size in the tree does -- see
+    /// `Len::dp`'s field doc. Only the `abs` component (folded from `dp` at
+    /// draw time, `Widget::draw` below) is meaningful here; `rel`/`rest`
+    /// were never supported for a gap and still are not.
+    pub gap: Len,
 }
 
 impl Widget for Span {
     fn draw(&mut self, painter: &mut Painter) -> Size {
         let axis = self.dir.axis;
+        let gap = self.gap.apply_rest(painter.density()).abs;
 
         // Phase 1: draw each child once, at the ambient (unmodified, full)
         // region a size-only query used to see before this migration, to
@@ -25,7 +31,7 @@ impl Widget for Span {
             .map(|child| painter.widget(child).axis(axis))
             .collect();
 
-        let gap_total = self.gap * self.children.len().saturating_sub(1) as f32;
+        let gap_total = gap * self.children.len().saturating_sub(1) as f32;
         let total = lens.iter().fold(Len::abs(gap_total), |s, &l| s + l);
 
         // Phase 2: place each child for real, using the lengths just
@@ -54,7 +60,7 @@ impl Widget for Span {
                 child_region.flip(axis);
             }
             let used = painter.widget_within(child, child_region);
-            start.abs += self.gap;
+            start.abs += gap;
 
             let ortho = used.axis(!axis);
             if ortho.rel > 0.0 || ortho.rest > 0.0 {
@@ -82,12 +88,12 @@ impl Span {
         Self {
             children: Vec::new(),
             dir,
-            gap: 0.0,
+            gap: Len::ZERO,
         }
     }
 
-    pub fn gap(mut self, gap: impl UiNum) -> Self {
+    pub fn gap(mut self, gap: impl Into<Len>) -> Self {
-        self.gap = gap.to_f32();
+        self.gap = gap.into();
         self
     }
 
@@ -103,7 +109,7 @@ impl Span {
 pub struct SpanBuilder<State, const LEN: usize, Wa: WidgetArrLike<State, LEN, Tag>, Tag> {
     pub children: Wa,
     pub dir: Dir,
-    pub gap: f32,
+    pub gap: Len,
     _pd: PhantomData<(State, Tag)>,
 }
 
@@ -129,13 +135,13 @@ impl<State, const LEN: usize, Wa: WidgetArrLike<State, LEN, Tag>, Tag>
         Self {
             children,
             dir,
-            gap: 0.0,
+            gap: Len::ZERO,
             _pd: PhantomData,
         }
     }
 
-    pub fn gap(mut self, gap: impl UiNum) -> Self {
+    pub fn gap(mut self, gap: impl Into<Len>) -> Self {
-        self.gap = gap.to_f32();
+        self.gap = gap.into();
         self
     }
 }

iris/src/widget/text/edit.rs

@@ -141,7 +141,8 @@ impl<'a> TextEditCtx<'a> {
     fn layout(&mut self) -> &Layout<UiColor> {
         let attrs = self.text.view.attrs.clone();
         let width = self.text.view.wrap_width();
-        self.text.view.buf.shape(self.data, &attrs, width);
+        let density = self.data.density;
+        self.text.view.buf.shape(self.data, &attrs, width, density);
         self.text.view.buf.layout()
     }
 
@@ -167,6 +168,20 @@ impl<'a> TextEditCtx<'a> {
         self.text.selection = None;
     }
 
+    /// [`set`](Self::set) plus a fresh set of [`SpanStyle`]s in one call --
+    /// what a streamed transcript row needs, since its markdown re-renders
+    /// to a new string *and* a new span list on every delta and the two
+    /// have to land together (a stale span list drawn against new text can
+    /// point past its end). Used by `transcript-ui`'s incremental apply
+    /// (RUST.md's "streaming still costs a full rebuild" fix) rather than
+    /// tearing the row's widget down and rebuilding it from scratch.
+    pub fn set_with_spans(&mut self, text: &str, spans: Vec<SpanStyle>) {
+        let text = self.string(text);
+        self.text.view.buf.set_text(text);
+        self.text.view.buf.set_spans(spans);
+        self.text.selection = None;
+    }
+
     pub fn motion(&mut self, motion: Motion, select: bool) {
         let Some(sel) = self.text.selection else {
             return;

iris/transcript-ui/src/composer.rs

@@ -39,7 +39,7 @@ where
         .label("Message")
         .add(rsc);
 
-    let bar: WeakWidget = (field.pad(12).width(rest(1)),)
+    let bar: WeakWidget = (field.pad(dp(12)).width(rest(1)),)
         .span(Dir::RIGHT)
         .background(rect(UiColor::new(40, 40, 46, 255)))
         .add(rsc);

iris/transcript-ui/src/lib.rs

@@ -60,6 +60,12 @@ pub struct TranscriptScreen {
     pub list: WeakWidget<List>,
     pub composer: composer::Composer,
     selection: Rc<RefCell<Selection>>,
+    /// How many times [`Self::apply`] has fallen back to a full rebuild --
+    /// `Cell` rather than requiring `&mut self`, matching every other
+    /// method here (the real state lives behind `list`/`selection`'s own
+    /// interior mutability, per `push_row`'s existing `&self`). Drained by
+    /// [`Self::take_rebuilds`].
+    rebuilds: std::cell::Cell<usize>,
 }
 
 impl TranscriptScreen {
@@ -75,6 +81,93 @@ impl TranscriptScreen {
         (self.list)(rsc).push_back(ListRow::new(key, widget));
     }
 
+    /// Apply the effect of one more folded event without rebuilding the
+    /// whole screen -- RUST.md's "streaming still costs a full rebuild"
+    /// fix. `old`/`new` are `client_core::transcript_fold::fold_event`'s
+    /// own before/after item lists (never grouped into rows -- that
+    /// happens here, over both, so the common tail cases can be told
+    /// apart; `group_tool_runs` is pure bookkeeping over already-folded
+    /// items, no widget is built doing it).
+    ///
+    /// Three cases, cheapest first:
+    /// - **nothing changed**: no-op.
+    /// - **pure append** (a still-open reply's row now closed and stable,
+    ///   a new tool call, a new message): every new row is `push_back`ed,
+    ///   same cost as [`Self::push_row`].
+    /// - **only the last row's content changed** (the common case: a delta
+    ///   folded into a still-open assistant message): that one row is
+    ///   rebuilt (`row::build_row`, the same path a fresh row goes
+    ///   through) and swapped in with [`List::replace_back`] -- every
+    ///   other row is untouched, so nothing else redraws or moves. Any
+    ///   further new rows are appended after it, for the (also common)
+    ///   case of a delta that both finishes the open reply and starts the
+    ///   next row in the same event.
+    ///
+    /// Anything else -- a row *before* the tail changed, which only
+    /// happens when `group_tool_runs` regroups already-seen items (a tool
+    /// run's calls that used to be separate rows join once the run closes)
+    /// -- falls back to a full rebuild: every row is dropped
+    /// (`List::clear`) and rebuilt from `new`. Counted in
+    /// [`Self::take_rebuilds`] so a caller (a report, a test) can see how
+    /// often the fallback actually fires rather than assuming it never
+    /// does.
+    pub fn apply<Rsc: HasEvents>(
+        &self,
+        rsc: &mut Rsc,
+        old: &[client_core::transcript_fold::TranscriptItem],
+        new: &[client_core::transcript_fold::TranscriptItem],
+    ) where
+        Rsc::State: FocusHost,
+    {
+        use client_core::transcript_fold::group_tool_runs;
+
+        let old_rows = group_tool_runs(old);
+        let new_rows = group_tool_runs(new);
+
+        match diff_rows(&old_rows, &new_rows) {
+            RowDiff::Unchanged => {}
+            RowDiff::Appended { common } => {
+                // Pure append: every already-drawn row is byte-for-byte the
+                // same `FoldedRow` it was last time.
+                for row in &new_rows[common..] {
+                    self.push_row(rsc, row);
+                }
+            }
+            RowDiff::ReplaceLast { common } => {
+                // Only the tail row's content changed -- rebuild that one
+                // row and swap it in place, keeping every row before it
+                // untouched.
+                let old_key = row::row_key(&old_rows[common].key());
+                let (new_key, widget) =
+                    row::build_row(rsc, self.list, self.selection.clone(), &new_rows[common]);
+                if new_key != old_key {
+                    self.selection.borrow_mut().unregister(old_key);
+                }
+                let evicted = (self.list)(rsc).replace_back(ListRow::new(new_key, widget));
+                drop(evicted); // frees the old row's widget, same as a pop would
+                for row in &new_rows[common + 1..] {
+                    self.push_row(rsc, row);
+                }
+            }
+            RowDiff::Rebuild => {
+                // A row before the tail changed (a regroup) -- nothing
+                // short of a full rebuild expresses that.
+                self.rebuilds.set(self.rebuilds.get() + 1);
+                (self.list)(rsc).clear();
+                for row in &new_rows {
+                    self.push_row(rsc, row);
+                }
+            }
+        }
+    }
+
+    /// How many times [`Self::apply`] has fallen back to a full rebuild
+    /// since the last call, reset to 0 by reading it -- the same
+    /// take-and-reset shape `AccessTree::take_rebuilds` already uses (I4).
+    pub fn take_rebuilds(&self) -> usize {
+        self.rebuilds.replace(0)
+    }
+
     /// The concatenated text of whatever is currently selected across one
     /// or more rows, `None` if nothing is -- what a copy command reads.
     pub fn selected_text(&self, rsc: &mut impl UiRsc) -> Option<String> {
@@ -139,7 +232,148 @@ where
             list,
             composer,
             selection,
+            rebuilds: std::cell::Cell::new(0),
         },
         tree,
     )
 }
+
+/// What changed at the tail between two folded row lists -- the decision
+/// [`TranscriptScreen::apply`] acts on. Kept as its own pure function, no
+/// widget and no `Rsc`, so the three cases can be tested directly against
+/// synthetic `Vec<FoldedRow>`s (below) rather than needing a full widget
+/// harness to exercise logic that never touches one.
+#[derive(Debug, PartialEq, Eq)]
+enum RowDiff {
+    /// `old` and `new` are the same length and every row is identical.
+    Unchanged,
+    /// Rows `[common..]` of `new` are new; everything before `common` is
+    /// byte-for-byte the same `FoldedRow` `old` already had.
+    Appended { common: usize },
+    /// Row `common` is the only one whose content differs; anything past
+    /// it in `new` is a pure append after the replacement.
+    ReplaceLast { common: usize },
+    /// A row *before* the tail differs -- only `group_tool_runs` regrouping
+    /// an earlier run does this, and nothing short of a full rebuild
+    /// expresses it.
+    Rebuild,
+}
+
+fn diff_rows(old: &[FoldedRow], new: &[FoldedRow]) -> RowDiff {
+    let common = old
+        .iter()
+        .zip(new.iter())
+        .take_while(|(a, b)| a == b)
+        .count();
+
+    if common == old.len() && common == new.len() {
+        RowDiff::Unchanged
+    } else if common == old.len() {
+        RowDiff::Appended { common }
+    } else if !old.is_empty() && common == old.len() - 1 && common < new.len() {
+        // The `common < new.len()` guard is what tells "the tail row's
+        // content changed" apart from "the tail row was removed and
+        // nothing replaced it" (a shrinking list) -- the latter has
+        // nothing at `new[common]` to rebuild into place.
+        RowDiff::ReplaceLast { common }
+    } else {
+        RowDiff::Rebuild
+    }
+}
+
+#[cfg(test)]
+mod diff_tests {
+    use super::*;
+    use client_core::transcript_fold::TranscriptItem;
+
+    fn user(seq: u64, text: &str) -> FoldedRow {
+        FoldedRow::Single(TranscriptItem::UserMsg {
+            seq,
+            text: text.to_string(),
+            attachments: Vec::new(),
+        })
+    }
+
+    fn assistant(seq: u64, text: &str, settled: bool) -> FoldedRow {
+        FoldedRow::Single(TranscriptItem::AssistantMsg {
+            seq,
+            text: text.to_string(),
+            settled,
+        })
+    }
+
+    fn tool(seq: u64, run_id: &str) -> TranscriptItem {
+        TranscriptItem::ToolRun {
+            seq,
+            id: format!("id{seq}"),
+            run_id: run_id.to_string(),
+            tool: "grep".to_string(),
+            input: "x".to_string(),
+            output: String::new(),
+            done: false,
+            asks: Vec::new(),
+            images: Vec::new(),
+        }
+    }
+
+    #[test]
+    fn identical_lists_are_unchanged() {
+        let rows = vec![user(1, "hi"), assistant(2, "hello", true)];
+        assert_eq!(diff_rows(&rows, &rows.clone()), RowDiff::Unchanged);
+    }
+
+    #[test]
+    fn an_empty_list_growing_by_one_is_an_append_from_zero() {
+        let old: Vec<FoldedRow> = Vec::new();
+        let new = vec![user(1, "hi")];
+        assert_eq!(diff_rows(&old, &new), RowDiff::Appended { common: 0 });
+    }
+
+    #[test]
+    fn a_new_message_after_a_settled_reply_is_a_pure_append() {
+        // The row that used to be the tail (a now-closed assistant
+        // message) is unchanged; a new user message is appended after it
+        // -- the transition every reply's *last* delta makes once the
+        // next turn starts.
+        let old = vec![user(1, "hi"), assistant(2, "hello", true)];
+        let new = vec![user(1, "hi"), assistant(2, "hello", true), user(3, "and?")];
+        assert_eq!(diff_rows(&old, &new), RowDiff::Appended { common: 2 });
+    }
+
+    #[test]
+    fn a_delta_into_the_open_reply_is_a_last_row_replace() {
+        // The common streaming case: the assistant message's key (its
+        // first delta's seq) never changes, only its text grows.
+        let old = vec![user(1, "hi"), assistant(2, "hel", false)];
+        let new = vec![user(1, "hi"), assistant(2, "hello", false)];
+        assert_eq!(diff_rows(&old, &new), RowDiff::ReplaceLast { common: 1 });
+    }
+
+    #[test]
+    fn a_delta_that_both_settles_the_reply_and_starts_the_next_row_is_still_a_replace() {
+        // `ReplaceLast` only claims the row it names; `apply` appends
+        // whatever comes after it separately -- this just confirms the
+        // diff still recognises the replace even with a trailing append.
+        let old = vec![user(1, "hi"), assistant(2, "hel", false)];
+        let new = vec![user(1, "hi"), assistant(2, "hello", true), user(3, "and?")];
+        assert_eq!(diff_rows(&old, &new), RowDiff::ReplaceLast { common: 1 });
+    }
+
+    #[test]
+    fn a_tool_run_closing_and_joining_an_earlier_call_is_a_regroup_fallback() {
+        // Two separate `Single` rows for the same run id become one
+        // `Tools` row once `group_tool_runs` sees them adjacent -- that
+        // changes row 0, not just the tail, so nothing short of a full
+        // rebuild expresses it.
+        let old = vec![FoldedRow::Single(tool(1, "run-a")), user(2, "meanwhile")];
+        let new = vec![FoldedRow::Tools(vec![tool(1, "run-a"), tool(3, "run-a")])];
+        assert_eq!(diff_rows(&old, &new), RowDiff::Rebuild);
+    }
+
+    #[test]
+    fn shrinking_the_list_is_a_rebuild() {
+        let old = vec![user(1, "hi"), assistant(2, "hello", true)];
+        let new = vec![user(1, "hi")];
+        assert_eq!(diff_rows(&old, &new), RowDiff::Rebuild);
+    }
+}

iris/transcript-ui/src/row.rs

@@ -60,6 +60,15 @@ fn item_content(item: &TranscriptItem) -> (Option<&str>, String) {
         TranscriptItem::PeerNote { from, text, .. } => (Some(from.as_str()), text.clone()),
         TranscriptItem::Note { text, .. } => (None, text.clone()),
         TranscriptItem::ClearedNote { .. } => (None, "_Context cleared._".to_string()),
+        // Epoch seconds as-is until the port has a relative-time formatter
+        // (P1); the Compose `LimitRow` draws it as a countdown.
+        TranscriptItem::LimitNote { resets_at, .. } => (
+            None,
+            match resets_at {
+                Some(at) => format!("_Usage limit reached; resets at {at:.0} (epoch seconds)._"),
+                None => "_Usage limit reached._".to_string(),
+            },
+        ),
         TranscriptItem::CompactedNote {
             pre_tokens,
             post_tokens,
@@ -165,8 +174,8 @@ where
 
     (header, field.width(rest(1)))
         .span(Dir::DOWN)
-        .gap(4)
+        .gap(dp(4))
-        .pad(10)
+        .pad(dp(10))
         .add_strong(rsc)
         .any()
 }

iris/transcript-ui/src/selection.rs

@@ -41,6 +41,12 @@ pub struct Selection {
     /// pan wanting the same touch gesture). See `drag` below, and
     /// `iris::sense::DragArbiter`'s own doc for the decision itself.
     arbiter: DragArbiter,
+    /// Tracks the last ~100ms of this gesture's pan deltas (in the same
+    /// signed units `list.scroll` takes), so a release that turns out to
+    /// have been panning can hand `List::fling` a realistic initial
+    /// velocity instead of one frame's noisy last delta --
+    /// IRIS_TODO.md's "swiping has no momentum."
+    velocity: VelocityTracker,
 }
 
 impl Default for Selection {
@@ -55,6 +61,7 @@ impl Selection {
             rows: BTreeMap::new(),
             anchor: None,
             arbiter: DragArbiter::new(),
+            velocity: VelocityTracker::new(),
         }
     }
 
@@ -178,9 +185,21 @@ impl Selection {
             CursorSense::PressStart(_) => {
                 let already_selected = self.has_selection(ui);
                 self.arbiter.press_start(pos_window, now, already_selected);
+                self.velocity.reset();
+                // A fresh touch-down cancels any fling still coasting from
+                // the previous gesture -- `List::fling`'s own doc, and
+                // Android's `Scroller::abortAnimation` for the same reason.
+                list(ui).cancel_fling();
                 self.arbiter.update(pos_window, now)
             }
             CursorSense::PressEnd(_) => {
+                // A fling only ever follows a pan -- never a selection
+                // that happened to end with the finger still moving, and
+                // never a tap/long-press that never left `Undecided`.
+                if self.arbiter.is_panning() {
+                    let v = self.velocity.velocity();
+                    list(ui).fling(v);
+                }
                 self.arbiter.release();
                 return;
             }
@@ -198,13 +217,19 @@ impl Selection {
             _ if self.arbiter.is_idle() => {
                 let already_selected = self.has_selection(ui);
                 self.arbiter.press_start(pos_window, now, already_selected);
+                self.velocity.reset();
+                list(ui).cancel_fling();
                 self.arbiter.update(pos_window, now)
             }
             _ => self.arbiter.update(pos_window, now),
         };
         match outcome {
             DragOutcome::Undecided => {}
-            DragOutcome::Pan(dy) => list(ui).scroll(-dy),
+            DragOutcome::Pan(dy) => {
+                let amt = -dy;
+                self.velocity.add_sample(amt, now);
+                list(ui).scroll(amt);
+            }
             DragOutcome::SelectStart => {
                 // Grep-able on "iris selection" the way the frame report is
                 // on "iris frame report" -- selection has no accessibility