Merge remote-tracking branch 'origin/main'

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

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

@@ -2,6 +2,7 @@ package com.example.aiapp
 
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.TextLinkStyles
 import androidx.compose.ui.text.font.FontFamily
@@ -10,6 +11,7 @@ import androidx.compose.ui.unit.TextUnit
 import com.mikepenz.markdown.m3.Markdown
 import com.mikepenz.markdown.m3.markdownColor
 import com.mikepenz.markdown.m3.markdownTypography
+import com.mikepenz.markdown.model.parseMarkdown
 
 /**
  * An assistant's reply, rendered as the markdown it is written in.
@@ -24,8 +26,22 @@ import com.mikepenz.markdown.m3.markdownTypography
 @Composable
 fun MarkdownText(text: String, modifier: Modifier = Modifier) {
     val body = MaterialTheme.typography.bodyLarge
+    // Parsed here, in the composition, rather than by the overload that takes the text itself.
+    // That one parses in a coroutine and draws an empty loading slot until the result arrives --
+    // so a row is measured at nothing before it is measured at its real height, and the
+    // transcript above it collapses and springs back. Seen with five replies on screen at once,
+    // every one of them blank, the whole conversation shrunk to fit a single screen; a moment
+    // later it was all there again. That is the "skipping up and down" this list must never do,
+    // and no amount of scroll anchoring can survive a row that lies about its height first.
+    //
+    // The cost is the parse on the main thread, which is the trade being made deliberately: a
+    // few milliseconds of work at the moment a row is composed, against a layout that is wrong
+    // every time one is. If a very long reply ever makes that visible, the answer is the
+    // renderer's streaming state -- which parses incrementally -- and not going back to a
+    // placeholder with no height.
+    val parsed = remember(text) { parseMarkdown(text) }
     Markdown(
-        content = text,
+        parsed,
         colors =
             markdownColor(
                 text = MaterialTheme.colorScheme.onSurface,

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

@@ -489,12 +489,41 @@ fun SessionScreen(
     var loadingHistory by remember { mutableStateOf(false) }
     var ready by remember { mutableStateOf(false) }
     val listState = rememberLazyListState()
+    // Whether the newest message is on screen right now. The list is laid out from the bottom
+    // (see the LazyColumn below), so "newest" is index 0 and being there is being at the start of
+    // it. This is what the jump-to-newest button watches: it is about what the reader can see.
+    //
+    // It is also the gate on everything the list draws -- see [record].
+    val atNewest by remember {
+        derivedStateOf {
+            listState.firstVisibleItemIndex == 0 && listState.firstVisibleItemScrollOffset == 0
+        }
+    }
+    // Transcript events that arrived while somebody was reading further back, in the order they
+    // arrived, waiting for them to return to the newest end. See [record] for why.
+    var held by remember { mutableStateOf(listOf<SeqEvent>()) }
     // What is actually drawn: the transcript with runs of adjacent tool
     // calls folded into one row each.
     val rows = remember(items) { groupToolRuns(items) }
 
-    fun apply(entry: SeqEvent) {
-        lastSeq.set(entry.seq)
+    /**
+     * Everything the transcript list draws, from one event.
+     *
+     * Separate from [apply] because it is the half that is allowed to wait. The list anchors on the
+     * leading edge of its first visible item, which in this upside-down layout is that item's
+     * *bottom* -- so a row that grows pushes everything already on screen upwards, and the view
+     * travels toward the newest end without anybody scrolling. Measured against a reply streamed in
+     * four hundred pieces: scrolling back a screen and then waiting six seconds ended at the very
+     * bottom, forty lines further on than where it was left.
+     *
+     * Insertions were never the problem -- the list is keyed, so a row arriving at either end
+     * leaves the anchor where it is, and reading back through history while a session works has
+     * always been still. What cannot be allowed is a row that is already there changing height, and
+     * the one guarantee that covers every way that happens -- a reply streaming, a tool's output
+     * arriving, a queued bubble appearing above the anchor -- is to change nothing at all while
+     * somebody is reading further back.
+     */
+    fun record(entry: SeqEvent) {
         // The oldest event this view holds, which is what paging backwards
         // starts from. Maintained here rather than by each loader: the
         // first page and a stream reset both begin an empty view, and one
@@ -503,6 +532,44 @@ fun SessionScreen(
             oldestSeq = entry.seq
             moreHistory = entry.seq > 1L
         }
+        val event = entry.event
+        // The message coming back is the session saying it has
+        // read it, so the bubble held below the indicator becomes
+        // the row `foldEvent` is about to add.
+        // Waiting, then read. Matched by id: the same message sent twice is two
+        // bubbles, and clearing by text would take away whichever matched first.
+        if (event is SessionEvent.MessageQueued) {
+            queued = queued + QueuedMessage(event.id, event.text, event.images)
+        }
+        if (event is SessionEvent.UserMessage) {
+            queued = queued.filterNot { it.id == event.id }
+        }
+        // Waiting, then gone: a command leaves this list when the session takes it,
+        // and the row it becomes is added by `foldEvent` in the same pass.
+        if (event is SessionEvent.CommandQueued) {
+            waitingCommands = waitingCommands + (event.id to event.text)
+        }
+        if (event is SessionEvent.CommandSent) {
+            waitingCommands = waitingCommands.filterNot { it.first == event.id }
+        }
+        // Kept as well as folded. Folding is one-way -- a tool's
+        // start and end become one row -- so a page arriving in
+        // front of what is already here cannot be stitched on
+        // without the events themselves.
+        loaded = loaded + event
+        items = foldEvent(items, entry)
+    }
+
+    /**
+     * One event, at the moment it arrives.
+     *
+     * What it says about the *session* -- running or not, which model, how many tokens -- lands
+     * immediately, because none of that is drawn in the list and freezing it would trade a
+     * transcript that jumps for a status row that lies. What it adds to the transcript goes through
+     * [record], which waits for the reader to be at the newest end.
+     */
+    fun apply(entry: SeqEvent) {
+        lastSeq.set(entry.seq)
         when (val event = entry.event) {
             // Taken, not accumulated: the server's running total is on the event, and adding
             // up the deltas this screen happened to receive counted one page of a conversation
@@ -532,34 +599,9 @@ fun SessionScreen(
                         }
                     status = event.state
                 }
-                // The message coming back is the session saying it has
-                // read it, so the bubble held below the indicator becomes
-                // the row `foldEvent` is about to add. Matched by text --
-                // all that distinguishes one message from an identical
-                // earlier one -- and only the first match, so two
-                // identical messages wait twice.
-                // Waiting, then read. Matched by id: the same message sent twice is two
-                // bubbles, and clearing by text would take away whichever matched first.
-                if (event is SessionEvent.MessageQueued) {
-                    queued = queued + QueuedMessage(event.id, event.text, event.images)
-                }
-                if (event is SessionEvent.UserMessage) {
-                    queued = queued.filterNot { it.id == event.id }
-                }
-                // Waiting, then gone: a command leaves this list when the session takes it,
-                // and the row it becomes is added by `foldEvent` in the same pass.
-                if (event is SessionEvent.CommandQueued) {
-                    waitingCommands = waitingCommands + (event.id to event.text)
-                }
-                if (event is SessionEvent.CommandSent) {
-                    waitingCommands = waitingCommands.filterNot { it.first == event.id }
-                }
-                // Kept as well as folded. Folding is one-way -- a tool's
-                // start and end become one row -- so a page arriving in
-                // front of what is already here cannot be stitched on
-                // without the events themselves.
-                loaded = loaded + event
-                items = foldEvent(items, entry)
+                // In order, always: one late event recorded ahead of the backlog would fold a
+                // streamed delta into whatever row happened to be last by then.
+                if (atNewest && held.isEmpty()) record(entry) else held = held + entry
             }
         }
     }
@@ -632,6 +674,7 @@ fun SessionScreen(
                                     // up pages the rest back in as it always does.
                                     items = listOf()
                                     loaded = listOf()
+                                    held = listOf()
                                     oldestSeq = 0L
                                     moreHistory = true
                                 },
@@ -659,12 +702,16 @@ fun SessionScreen(
     // stays started.
     DisposableEffect(summary.id) { onDispose { activeStream.get()?.close() } }
 
-    // Whether the newest message is on screen right now. The list is laid out from the bottom
-    // (see the LazyColumn below), so "newest" is index 0 and being there is being at the start of
-    // it. This is what the jump-to-newest button watches: it is about what the reader can see.
-    val atNewest by remember {
-        derivedStateOf {
-            listState.firstVisibleItemIndex == 0 && listState.firstVisibleItemScrollOffset == 0
+    // Back at the newest end, so the backlog [apply] held can land. Everything at once rather
+    // than paced out: they are at the bottom, which is the one place the list is allowed to
+    // follow new content, and drip-feeding it would only make that following last longer.
+    LaunchedEffect(listState) {
+        snapshotFlow { atNewest && held.isNotEmpty() }
+            .collect { due ->
+                if (!due) return@collect
+                val backlog = held
+                held = listOf()
+                backlog.forEach { record(it) }
             }
     }
     // Whether they *chose* to be there, which is a different question and the one that decides

server/src/session/echo.rs

@@ -25,6 +25,9 @@
 //! This is exactly the event vocabulary the real drivers produce, so a UI
 //! that renders echo sessions correctly renders the real thing.
 //!
+//! - `/stream N` -- one long answer in N small pieces, 50ms apart: the
+//!   shape a real model's reply arrives in, and the one where the row a
+//!   reader is anchored to is the row that keeps changing height.
 //! - `/mixed N` -- N beats of an interleaved transcript: paragraphs of
 //!   different lengths, single tool calls, runs of adjacent ones, images
 //!   and a peer message. Rows of every shape and height the app draws, in
@@ -338,6 +341,9 @@ impl EchoDriver {
         // rather than trusted: this is a test affordance, and a session
         // pinned running for an hour by a typo is a worse outcome than a
         // short wait.
+        let stream = text
+            .strip_prefix("/stream")
+            .map(|rest| rest.trim().parse::<usize>().unwrap_or(400).clamp(1, 4000));
         let mixed = text
             .strip_prefix("/mixed")
             .map(|rest| rest.trim().parse::<usize>().unwrap_or(12).clamp(1, 400));
@@ -423,6 +429,23 @@ impl EchoDriver {
                 return;
             }
 
+            // One long answer arriving in small pieces, which is what a real
+            // model does and what `/slow` does not: `/slow` emits a line a
+            // second, so its message grows in steps a reader can watch one
+            // at a time. A jump caused by the *anchor row itself* changing
+            // height needs growth that is continuous.
+            if let Some(pieces) = stream {
+                for i in 0..pieces {
+                    let len = 3 + (i * 7) % 14;
+                    send(Event::AssistantText {
+                        delta: format!("{i}{} ", "x".repeat(len)),
+                    });
+                    tokio::time::sleep(Duration::from_millis(50)).await;
+                }
+                finish();
+                return;
+            }
+
             if let Some(beats) = mixed {
                 for beat in 1..=beats {
                     write_beat(&sink, &dir, beat).await;