ai-app/RUST.md

Moving the app to Rust

Working document for the question Iris asked on 2026-09-04: what are the options for switching the phone app to Rust, ideally pure Rust with one UI framework shared with a future winit-based desktop application, at full feature parity and without giving up anything native, performance especially. Constraints she set: no Dioxus and nothing that draws through a WebView; no UI DSL (which rules out Makepad and Slint); the result should stay lightweight; platform-specific pieces are fine to maintain; reimplementing a framework piece from scratch where it does not fit is fine; effort and elapsed time do not matter, long-term robustness does; this clone is where things get tried before anything is committed to ai-app. Her own library, iris, is the in-house framework to be built up for this, with Masonry as the yardstick it is measured against.

Decisions get a date and a reason here, the way PLAN.md does. A section describes something that has been tried only where it says so, with a date.

Keep this file current as you work

This file is the handoff, and it is meant to let a session be cleared. Write each result into it as you get it, not at the end: the box ticked or the reason it could not be, the measurement with its number, the decision with its date and what it rejected, and anything that cost time to find out. Then a session that has filled its context can be cleared and the next one can pick up from this file alone, which is much cheaper than carrying a long conversation or re-deriving what was already measured.

Two things that follow. Write for somebody who was not here — name the command, the file and the number rather than "the fix" or "the earlier run". And write the failures and the dead ends too: "Venus is blocked by the emulator, not by Mesa" and "the present mode was not the cause" are worth as much as the successes, because they are what stops the next session spending an afternoon on them again.

Where things stand (2026-09-04)

• Done: E0 (toolchain), E1 (Masonry on android-view, which found the keyboard gap — now explained, see below), I0a, I0b (iris builds on a pinned nightly and runs), I1 (parley + glyph atlas).
• Done, 2026-09-04: the Widget::draw/layout redesign (LAYOUT.md). desired_width/desired_height/SizeCtx/Cache are gone; every widget in iris/src/widget/ implements one fn draw(&mut self, &mut Painter) -> Size. A moved widget (Scroll, Offset) now costs one move_offsets write resolved by a shared resolve_move WGSL function in both shader stages, independent of how many primitives are in its subtree — measured at 500 in iris/src/layout_tests.rs, which also covers the unchanged-frame, hit-test-after-move and mask-follows-move pass conditions as plain unit tests (no GPU or window needed, since UiRenderState touches neither). All four examples render pixel-identically to before the change. See LAYOUT.md's "Deviations found during implementation" for five real bugs the design's first draft did not anticipate — worth reading before touching Aligned, Sized, MaxSize, Scroll, or the move-slot lifecycle again. GpuTextures::grow_array (a second atlas layer opening) has now been exercised too, on tabs with PAGE temporarily lowered — see TEXTURES.md's "Exercised, 2026-09-04". Not done: a pixel-level screenshot check of a Masked-wrapped Scroll (no example builds one yet — the numeric check in layout_tests.rs stands in).
• E1's keyboard gap is Masonry's as_input_connection returning None (a TODO), not android-view or EditorInfo. android-view's own demo implements the InputConnection trait over a parley editor and gets real Gboard suggestions on this emulator — screenshotted 2026-09-04. android-view's accesskit_android adapter also has a reproducible abort (a client detaching, not attaching, is the trigger) — see E1 below for both, with the mitigation iris/I4 needs to carry.
• Resolved, 2026-09-04: iris's binding array does not survive real Android hardware. iris's texture pipeline used to ask every device, unconditionally, for VK_EXT_descriptor_indexing ("bindless" binding arrays), which a real share of Android hardware lacks. It has been rebuilt per TEXTURES.md's "Recommended shape": the glyph atlas is one texture_2d_array (a layer per page), a standalone image is its own ordinary Texture/BindGroup, and request_device now asks for no features and no binding-array limits at all. rigs/gpu-probe, rewritten to match, confirms request_device now succeeds on the emulator's software Vulkan (EMU_GPU=software, SwiftShader) — see TEXTURES.md's "Implemented, 2026-09-04" for the exact command and output, and for what was verified (rendering, via run-headless.sh) versus what was reasoned through but not separately stress-tested (a real second-atlas-page grow under load). Nothing here has been run on real Android hardware yet, only the emulator; the Android Vulkan Profile 2025 sourcing in "iris's binding array does not survive real Android hardware" below is what stands in for that until I2 gets a device.
• I2 — iris on android-view: done 2026-09-05. The android-view backend (iris/src/android/), the iris-android-app cdylib and Gradle shell, insets, the back gesture, and the full InputConnection bridge are all in and measured working — Gboard's suggestion strip reads real buffer content through it, the same bar E1 set. The render gap (nothing drew but the clear colour) is fixed: UiRenderNode::new seeded the GPU's window uniform from WindowUniform::default() (0, 0) rather than the surface's real size, so the vertex shader's / window.dim produced NaN/Inf clip positions on every primitive, on both Vulkan and GLES — winit's backend never hit this because winit fires an initial WindowEvent::Resized that corrects it before the first frame, and android-view has no equivalent event. Fixed by seeding the uniform from config.width/height at construction instead of depending on a later resize call. The tabs example now renders on the emulator on both backends (screenshotted); the GLES-only D2/D2Array warning was confirmed a red herring — still present post-fix, harmless. See I2's own entry below for the full writeup. E2 (a transcript in Masonry) can go in parallel in another session.
• client-core built (2026-09-04), item 1 of the recommendation: event-model/ (the event types, now shared with server/) and client-core/ (REST and SSE clients, transcript fold, cache, highlighter, ANSI parser, 85 ported tests). CLIENT_CORE.md maps Kotlin file to Rust module and lists what is not yet covered. ./run-tests.sh runs all three crates.
• The app itself is untouched. Everything so far is in iris/, in rigs/gpu-probe (a headless wgpu/Vulkan feature probe, pushable to a device with no APK — see the binding-array section), and in the other rigs; nothing under app/ or server/ has changed.
• Changed outside this repo, both in emulator-tools and both pushed: avd_serial now validates its cache by asking the device its AVD name rather than by checking the serial is still attached (a recycled port silently pointed this checkout at another session's emulator), and EMU_GPU=software was added as an opt-in that keeps a run off the host GPU and gives the guest a software Vulkan device. The default is unchanged, because -gpu host was measured and the Compose benchmarks depend on it.

What has to be reproduced

The app is ~19,000 lines of Kotlin. It splits three ways, and the split is what decides how much of a port is mechanical.

Pure logic with no Compose or Android in it, ~4,500 lines. Api.kt (1,142), Events.kt, EventStream.kt, Sse.kt, TranscriptCache.kt (589, touches java.io.File only), TranscriptSource.kt, MarkdownSyntax.kt, Languages.kt, Highlighter.kt, Ansi.kt, ResetCountdown.kt, Durations.kt, Sizes.kt, ModelName.kt, LoadState.kt, ImportableStream.kt. TranscriptUnits.kt and TranscriptItems.kt (the event fold into rows, ~940 lines) are logic with a handful of Compose annotations. This is also exactly the code that has JVM unit tests today. All of it ports directly, and most of it already has a Rust twin in server/: Events.kt is a hand-kept mirror of session/driver.rs's enum, the highlighter and the syntax scanner exist on the server for the explorer, and the cache compares the server's own JSON lines. Sharing these types between server and app is the single largest "keep things in sync" win available, and it does not depend on which UI framework wins.

Compose UI, ~13,000 lines. Screens, dialogs, the transcript list, the markdown renderer's customisations, tool cards, the file explorer viewer and editor. This is the part a UI framework choice is about.

Android platform code, ~1,500 lines, spread over 20 files. Every one of these is a Java-side object that no Rust framework can replace, because Android only offers them as Java classes:

• NotificationService — a foreground service holding the /notifications SSE stream while the app is closed, with its ongoing notification, specialUse type and the POST_NOTIFICATIONS request.
• MainActivity — edge-to-edge, the ACCESS_LOCAL_NETWORK runtime permission (Android 17), singleTop intent routing for aiapp://enroll, notification taps, and the share sheet (ACTION_SEND, any MIME type).
• ServerConfig — the bearer token sealed under an Android Keystore AES-GCM key, shared with Dev Updater through wg-app-link's :link.
• EnrollmentScanActivity — the in-app QR scanner (zxing, camera).
• Attachments — ContentResolver reads of shared URIs, BitmapFactory decode and downscale, EXIF orientation.
• SessionImage — bitmap decode for produced images.
• ScrollAnchor, Drafts — SharedPreferences; CrashLog — filesDir.
• TranscriptCache — cacheDir.
• DebugStats/FrameStats — Choreographer frame timing and the render report; runtime-tracing names composables in a system trace.

So "pure Rust" on Android means Rust owns every line of logic and drawing, behind a thin shell of Java stubs, and a packaging step that produces a signed APK. How thin, and whether Gradle is inevitable, are answered below.

How much Java is unavoidable, and why

Rust can call any Android API through JNI (jni crate, with ndk-context handing over the JavaVM and the Activity): posting a notification, startForegroundService, the Keystore, ContentResolver reads, permission requests, WindowInsets, the clipboard. None of that needs a line of Kotlin. What JNI cannot do is define a class that the system instantiates by name from the manifest — an Activity, a Service, an Application, a BroadcastReceiver. Those must exist as dex bytecode inside the APK before any Rust runs, because the framework constructs them and only then calls into native code. NativeActivity is the platform's own stub for the Activity case; there is no NativeService, and android-view ships its own View subclass for the same reason.

So the floor is roughly two Java classes of ten lines each: an Activity and a Service whose lifecycle methods are declared native and registered from JNI_OnLoad, plus whatever android-view already provides. Everything they would have done in Kotlin — insets, intent routing, the SSE follow loop, the notification builder — is Rust reached through those stubs. Writing the stubs in Java rather than Kotlin drops kotlinc from the toolchain; javac comes with the JDK Gradle already needs. Generating the dex from Rust is not worth it: there is no mature Rust dex writer, and the stubs never change.

Can the APK be built without Gradle?

Yes. An APK is a zip containing a binary-XML AndroidManifest.xml, resources.arsc, classes.dex, lib/<abi>/*.so and assets, aligned and signed with the v2 scheme. The tools are aapt2 (manifest and resources), d8 (Java bytecode to dex), zipalign and apksigner, all in the SDK's build-tools, none of them Gradle. Three ways to drive them:

• A cargo xtask (or build.rs-adjacent script) that runs cargo ndk for each ABI, javac + d8 for the stubs, aapt2 link, zipalign, apksigner. About 150 lines, every step visible, no AGP, no Gradle daemon holding 2.8 GB between builds. The pinned-CA constant becomes a build.rs reading the same certs/ca.pem path.
• cargo-apk2: the maintained successor to cargo-apk, and unlike it compiles java_sources / kotlin_sources into the dex and declares multiple activities and services with intent filters from [package.metadata.android], with per-profile keystores and optional aapt2. Exactly the shape needed; the question is whether a third-party tool with one maintainer beats 150 lines we own.
• cargo-apk / xbuild: unmaintained and NativeActivity-only. No.

What Gradle would take with it: Android Lint (which found two real bugs here, but in Kotlin that would no longer exist — with forty lines of Java stubs there is little left for it to find), manifest merging, R8, and the generated-source plumbing. What it gives back: one toolchain, cargo end to end, and Dev Updater keeps calling build-apk.sh exactly as now. Recommendation: the xtask, with cargo-apk2 read for the details it already got right (v2 signing, uses-feature, ABI splits).

The behaviours that are hard to get back

Reading the Compose code for what a replacement must be able to express, rather than what it happens to look like:

1. The transcript is one selectable body of text. One SelectionContainer around the whole lazy list, so a selection runs from a reply into the tool output beneath it. The framework needs selectable read-only rich text across many rows, with the platform's selection handles and clipboard on the phone.
2. Rich inline text: markdown with links (one tap detector per text, not a node per link), inline code chips drawn behind the text, tables with wrapping cells and a sideways scroll, syntax-highlighted fences, ANSI colour in tool output, Nerd Font icon glyphs. Needs a text layout engine with spans, not just styled labels.
3. A bottom-anchored virtualised list of variable-height rows, paged in both directions (800-event pages, HISTORY_SCREENS measured in viewports), with a saved scroll anchor per session, "hold the edge nearest the tap" when a row expands (holdTopEdge, done in the layout pass so the wrong frame is never drawn), and rows keyed so that a run of tool calls stays one row while it grows.
4. The soft keyboard: the composer resizes with the IME, the guard against a stuck inset animation, drafts per session, autocorrect and suggestions from the phone's own keyboard. This is where most Rust frameworks fail on Android today; see below.
5. Platform integration through the app model: foreground service, notifications, share sheet, deep link, Keystore, camera, back gesture, edge-to-edge insets, local-network permission.
6. Accessibility names on icon buttons, which the bench scripts depend on (ui-trace taps by label). A framework with no accessibility tree also breaks the measuring rig.
7. Measurable frames: the debug render report, and a way to attribute a frame's cost to a widget on the real phone.

The two constraints that decide it

1. Android text input. Every framework built on winit inherits winit's Android backend, and that backend cannot drive the soft keyboard properly: the IME tracking issues (#1823, #2766) are open, ReceivedCharacter is unimplemented on Android (#2305), and the android-activity groundwork for editor actions only merged in February 2026 (PR #214) with the winit half still to come. Composition, autocorrect and suggestions need an InputConnection implemented on the Java side, which winit's NativeActivity/GameActivity model does not offer. The frameworks that type on Android today each wrote their own Java glue (Slint, Makepad), and the one designed to do it the way Android intends is android-view: a Rust implementation of an Android View, with text input through InputConnection, accessibility, touch, callbacks on the UI thread, usable either as a whole app or embedded beside ordinary Android components. It is marked WIP. Both Linebender (its Masonry demo lives in that repo) and Robius/Makepad (Robrix's release notes say Android lacks a "full" keyboard and they are integrating android-view for it) are converging on it. That makes android-view the phone-side foundation whichever widget set sits on top, and the first thing to build and measure here.

2. Rich, selectable text and a virtualised list. Frameworks group by their text stack:

• Parley + Fontique + Vello (Linebender): rich spans, selection and editing utilities, IME support driven through ui-events, AccessKit text properties (Linebender 2026 Q1, parley). Used by Masonry/Xilem, and by Blitz. Vello proper needs compute shaders; vello_hybrid (CPU path processing, GPU compositing) is "roughly beta" and runs on GLES too, and Vello CPU exists as a no-GPU fallback.
• cosmic-text (iced, egui optionally): good layout, but the widgets on top decide selection. iced's markdown widget is not selectable (discourse).
• Slint's own: TextInput with read-only is the selectable-text trick; there is no inline rich text at all (issue #1325, markdown request #6684 both open). A markdown transcript with links and code chips cannot be drawn.
• Makepad's own: GPU/SDF text, a Markdown widget and a virtualised PortalList in makepad-widgets.

Options

A. Keep Compose, move the logic into a Rust core (uniffi)

A client-core crate (events shared with the server, API client, SSE, transcript fold, cache, markdown model, highlighter, ANSI) exposed to Kotlin through uniffi. Compose keeps drawing. Desktop would be a second UI (iced or Compose Desktop) over the same core.

• For: the logic and the wire types stop drifting from the server today, with tests in one language. Incremental and always shippable.
• Against: it is not what was asked for. The 13,000 lines of UI stay Kotlin, the desktop app shares no UI code, and the :link Kotlin module stays. uniffi's Kotlin Multiplatform bindings are a community fork; the Android-only bindings are Mozilla's and solid.
• Verdict: not the destination, but step one of every other option is building this crate, so it costs nothing to keep it as the fallback.

B. Slint

Rust on Android is officially supported (minSdk 26, android-activity backend, own Java IME glue, safe areas and keyboard insets since 1.15, Skia renderer needs clang). Royalty-free licence requires disclosing Slint use; GPLv3 otherwise. UI is a separate .slint DSL, not Rust.

• Against: no rich inline text (see above), so the transcript cannot be drawn as it is today; the UI language is not Rust, which forfeits the "compiler catches it" motivation for the half of the code that is UI.
• Verdict: rejected on rich text alone.

C. iced

Elm-style, Rust-only widgets, desktop-first, winit + wgpu. Has a markdown widget and rich_text with links. The maintainer states mobile is a non-goal (iced); a community Android example exists and its author could not get the soft keyboard working, patched widgets for touch, and notes no accessibility (HN thread). Markdown is not selectable; scrollable is not virtualised.

• Verdict: a fine desktop toolkit and the one Iris named, but every phone-side gap (IME, touch, accessibility, selection, virtualisation) would be ours to build and maintain against a project that does not want them. Not the shared framework.

D. egui

Immediate mode, winit-based on Android, AccessKit integration, selectable labels across a Ui. Repaints only on input by default, so battery is not the immediate-mode worry. Android IME is blocked on winit (discussion); the workaround is an in-app virtual keyboard, which is exactly the non-native keyboard to avoid. Variable-height virtualised lists are manual (show_rows assumes uniform heights). Looks like egui, not Material.

• Verdict: workable on desktop, wrong on the phone for the same reason as iced, plus a look that would need a full custom style.

E. Makepad

GPU-rendered, hybrid retained/immediate, live_design! DSL with hot reload, MIT, 1.0 in 2025 (makepad). Ships Android apps today with its own Java glue; Robrix (a Matrix chat client, the closest analogue to this app) is its reference application on Android, iOS and desktop. Has Markdown, PortalList (virtualised), TextInput. Robrix reports the Android keyboard is not "full" and is moving to android-view for it; the README says non-standard targets "may require minor fixes".

• For: the only option that already ships a chat-shaped app on Android and desktop from one codebase, with the widgets this app needs.
• Against: the DSL is its own language with its own shader-based styling, so a large part of the UI would not be checked by rustc; the rendering model (SDF everything) is a different world from Compose's, and selection across a Markdown widget is unverified.
• Verdict: rejected 2026-09-04 — Iris does not want a DSL. Kept here so its Android keyboard status stays a data point about android-view, not as an option.

F. Masonry / Xilem on android-view (Linebender)

Retained widget tree (Masonry) with a reactive view layer (Xilem) that reads like Compose; Rust all the way down; Vello, Parley, Fontique, AccessKit, ui-events. Widgets include Prose (selectable read-only rich text), TextArea, VirtualScroll, and this year Svg, Split, CollapsePanel, a new layout system, and IME through ui-events independent of winit. masonry_android_view exists in the android-view repo and is "not yet generally usable"; Xilem calls itself experimental. Desktop runs on winit. Vello needs a compute-capable GPU or falls back to vello_hybrid/CPU.

• For: the only stack where every hard behaviour above maps onto a component designed for it: selection and rich text (Parley/Prose), virtualised variable heights (VirtualScroll), native IME (android-view's InputConnection), accessibility (AccessKit, now with an Android crate), one Rust widget language on both platforms. The team is the one writing the Android integration everyone else is adopting.
• Against: pre-1.0 with API churn each release; a small team; no Material widget set, so every control's look is ours; some of the pieces (masonry_android_view, vello_hybrid) are explicitly unfinished. Being early means fixing things upstream ourselves, which Iris said is acceptable.
• Verdict: the option to try first, because it is the only one whose gaps are "not finished yet" rather than "not designed for this".

G. iris — the in-house library, and what "from scratch" means here

cat16/iris, read 2026-09-04 from the one public commit (2026-01-31, "portfolio copy"; ~8,700 lines in core, macro and the crate itself). Retained-mode widgets stored outside the render tree, wgpu 28 directly, winit 0.30, cosmic-text 0.16 (parley since I1), a relative-anchor-plus-offset layout with rest() and rel() lengths, a postfix builder API (rect(..).radius(30).on(CursorSense::click(), ..) .sized(..).align(..)), events handled where the widget is declared, and a single-threaded context passed explicitly — all of which reads like this codebase's own rules. There is text editing (widget/text/edit.rs), images, masks, spans and stacks; the TODO names text resizing as per-frame slow and scaling as unsolved. It requires nightly (fourteen #![feature] gates as vendored, among them const_trait_impl, unboxed_closures, portable_simd, associated_type_defaults; eleven after I0b and I1 — see those steps for the current list). Desktop only; no Android surface, no IME, no accessibility tree, no virtualised list, no rich-text selection.

That list is the work, and some of it is done. As of 2026-09-04 it builds on a pinned nightly, runs on this machine's GPU, has parley and a glyph atlas, and iris-core cross-compiles to Android. What it still lacks from the list above is the Android surface, the IME bridge, the accessibility tree and the virtualised list — I2, I3 and I4.

iris is not a candidate to be tested as it stands. It is the in-house library (Iris, 2026-09-04): "essentially a good start to a rewrite from scratch", to be maintained and extended by the sessions working here. So the list above of what it lacks is a work list, not a score. When the app needs something iris does not have, the answer is to build it into iris. The layer iris has is the widget and layout layer; the layers it needs are the same ones Masonry gets from android-view, Parley and AccessKit, and there is no reason iris cannot sit on those same foundations rather than reinvent them — the surface, the keyboard bridge and the accessibility tree are platform plumbing, not a framework's identity. The text stack was the first real design decision in that work, and it is settled: Parley, with a glyph atlas (I1, 2026-09-04).

Two things to carry into that work honestly. Nightly is the opposite of "holds up long term": a build that breaks on a toolchain update, on the machine Dev Updater builds on, unattended. Done in I0b — iris/rust-toolchain.toml pins nightly-2026-09-03 — and the gate list lives with I0b and I1, to be retired as they stabilise or are designed around; it is down from fourteen to eleven. And a one-person framework carries every gap itself, which is what Iris said she is willing to do.

"From scratch" therefore means iris, not a fourth thing. Masonry stays in the plan as the yardstick and the fallback: building its demo and its version of the transcript screen first says what a finished stack costs on this hardware, proves android-view before iris depends on it, and gives a comparison that is measured rather than remembered.

Not considered further: GPUI (Zed) mobile is a community fork that depends on unpublished crates; Dioxus/Blitz is excluded by Iris (its native renderer is Parley/Vello under HTML semantics, and the earlier tdep-survey/app-dioxus spike parked it on a vello_hybrid stroke bug and shipped the WebView); Compose Multiplatform Desktop would give a desktop app for nothing but in Kotlin, which is the opposite direction.

Weight and debug builds

Iris remembers the Linebender stack being slow in debug. What is behind that is the dependency graph — Vello, wgpu, Parley, Fontique, Skrifa — running unoptimised on the CPU side (path encoding, shaping), not the widget layer. Xilem's own advice is only split-debuginfo = "unpacked" to keep target/ small; the fix everyone with this shape of dependency tree uses is to optimise dependencies while leaving the app crate at opt-level = 0:

[profile.dev.package."*"]
opt-level = 2

Measured 2026-09-04, and it is not the widget layer. iris's own graph (wgpu + winit + cosmic-text at the time) built cold in 43s with a 2.1 GB target/, and 1m46s with a 1.5 GB target/ under the profile above — so the knob costs build time and saves disk here, and plain debug was never the problem. Masonry's graph is the one with Vello, Parley, Fontique and Skrifa in it, and E1 gives the number that matters for it: libmain.so is 181 MB in debug and 11 MB in release. That size is also a correctness issue rather than only a weight one — a debug build labels its Vulkan objects, and the emulator's driver segfaults in SetDebugUtilsObjectNameEXT when it does. Runtime cost of the profile knob is still unmeasured; resident memory and the frame cost of an 800-event page want E2. Vello proper needs compute shaders and carries a large shader set; vello_hybrid is lighter and Masonry can now render through either (or Vello CPU) via its imaging abstraction, so "keep it light" has a knob inside the same stack.

Recommendation

1. Build client-core now, whatever the framework (done 2026-09-04, see CLIENT_CORE.md). A Rust crate holding the event model (shared with server/ as one crate, ending the Events.kt mirror), the API and SSE clients, the transcript fold, the cache, the markdown block model, the highlighter and the ANSI parser, with the existing JVM tests ported. It is the part of the app that is already tested, already logic, and already duplicated on the server.
2. One foundation, two widget layers. The platform plumbing is shared whichever way the decision goes: android-view for the Android surface, keyboard and accessibility bridge; wgpu for the GPU; AccessKit for names; winit on the desktop. On top of it, Masonry as the yardstick (E1, E2) and iris as the thing being built (I0–I5), both aimed at the same transcript screen with the same pass conditions.
3. Decide when the transcript screen exists in both, from the measurements, and record the decision here with the numbers. If iris carries the screen within the Compose baseline, it is the app's framework and Masonry was the calibration. If it does not, the measurement says which parts of Masonry to adopt underneath it.
4. Then the shell (E3), the desktop window (E4) and the packaging (E5), which do not depend on the choice.

Experiments, in order

Each has a pass condition that is a measurement in this clone. The rig matters: this emulator runs -gpu host with host Vulkan switched off (GPU_HOST_FEATURES in emulator-tools, a gfxstream/Venus gap), so inside the guest a wgpu app gets GLES, not Vulkan; the earlier Dioxus spike also needed WGPU_GLES_MINOR_VERSION=1 for compute shaders and found wgpu's Android backend wants API 26 (a libc symbol). The real phone has Vulkan. Per the standing rule, a rig limit is something to fix before it is accepted.

• E0 — toolchain (done 2026-09-04). Installed under the user-owned SDK: NDK r29 (29.0.14206865), 2.4 GB at ~/Android/Sdk/ndk/29.0.14206865, the newest stable — r30 is still at rc.3. cargo-ndk 4.1.2. Verified by cross-compiling a scratch cdylib to both ABIs: file reports "for Android 26, built by NDK r29 (14206865)" for aarch64-linux-android and x86_64-linux-android. Two things to know at the call site. cargo-ndk 4's API-level flag is -P, not -p — -p is now passed through to cargo as --package, so the old cargo ndk -t arm64-v8a -p 26 panics with unknown package: 26 and dumps the whole environment to stdout as a bug report, which is worth not doing in a log somebody might paste. And the Android targets were installed for stable only; the pinned nightly needs its own, which iris/rust-toolchain.toml now declares.

• E1 — android-view's Masonry demo on this emulator (2026-09-04). It builds, renders on the GPU through Vulkan, exposes its accessibility tree, and the phone's own keyboard types into its editor — but with no autocorrect and no suggestions. Ticked because everything it was meant to establish is established, including the one gap; that gap is now E2's problem and I2's.

  *Build.* `~/src/android-view` at `bec6c62`, x86_64 rather than the
  README's arm64 because that is what this emulator is:
  `cargo ndk -t x86_64 -P 26 -o masonry-app/src/main/jniLibs/ build -p
  android-view-masonry-demo --release`, then
  `./gradlew :masonry-app:assembleDebug`. **`libmain.so` is 181 MB in
  debug and 11 MB in release** — the loudest single number about
  Vello's dependency graph, and the reason the release build matters
  for more than speed.
  
  *Renderer.* wgpu takes **Vulkan**, and the emulator log confirms it
  from the other side: `Created VkDevice ... for application:'wgpu'`.
  Two things were needed. The emulator must be given Vulkan at all —
  `-feature Vulkan` with `VK_DRIVER_FILES` pointing at the SDK's
  `vk_swiftshader_icd.json`, **plus `-no-snapshot-load`**, which is the
  piece this file had flagged as untested: without a cold boot the
  guest keeps the snapshot's old GPU config and `cmd gpu vkjson`
  reports zero devices however the host is configured. And the native
  library must be **release**: a debug build calls
  `SetDebugUtilsObjectNameEXT` to label its image views, and the
  emulator's own guest driver (`vulkan.ranchu.so`) segfaults inside it.
  On GLES, with no Vulkan available, it instead fails
  `Surface::configure` with "Invalid surface" — untriaged, since the
  Vulkan path works and Vello wants compute shaders anyway.
  
  *Accessibility works*, which E2's condition 6 and every bench script
  depend on. `ui-trace` reads Masonry's AccessKit tree: "Add task"
  arrives as a named `Button`, the editor as an `EditText` node. So
  tap-by-name works against a Masonry screen for any control carrying
  a name; the demo's editor carries none, which is the demo's omission
  rather than the framework's.
  
  *The keyboard: real input yes, suggestions no.* Tapping the editor
  opens the actual soft keyboard (`mInputShown=true`, Gboard), and
  tapping its keys types into Masonry — "teh" typed key by key, with a
  caret. What does **not** appear is Gboard's suggestion strip. The
  control is what makes that a finding rather than an impression: the
  **same three key taps in the Settings app's search field, on the same
  device in the same session, produce "teh | the | yeh"**. So the strip
  works here and android-view's editor is not asking for it — most
  likely the `EditorInfo` its `InputConnection` reports. That matches
  Robrix's report that the Android keyboard is not yet "full", and it
  is the single most important thing to fix or fund upstream, because
  composition, autocorrect and suggestions are exactly what the
  composer in this app needs and exactly what `winit` cannot do at all.
  
  **Cause found 2026-09-04, and it is Masonry's, not android-view's.**
  `~/src/android-view/masonry/src/lib.rs:531` is
  
      fn as_input_connection(&mut self) -> Option<&mut dyn InputConnection> {
          // TODO
          None
      }
  
  so the Masonry demo has **no `InputConnection` at all**; `RustView`
  returns null from `onCreateInputConnection` and the IME falls back to
  dispatching raw key events, which is exactly the behaviour observed —
  keys arrive, composition does not exist, so there is nothing for
  Gboard to suggest against. It is not a wrong `EditorInfo`, and the
  guess above that it was is withdrawn.
  
  android-view's **own** demo (`demo/src/lib.rs`, packaged by `app/`)
  implements the whole trait against a parley editor and asks for
  `INPUT_TYPE_CLASS_TEXT | CAP_SENTENCES | AUTO_CORRECT | MULTI_LINE`
  with `IME_FLAG_NO_FULLSCREEN | NO_EXTRACT_UI | NO_ENTER_ACTION`
  (`demo/src/lib.rs:588`). So the capability is present in the layer
  iris would sit on, and the 30-odd method `InputConnection` trait in
  `src/ime.rs` — `set_composing_text`, `set_composing_region`,
  `finish_composing_text`, `text_before_cursor`, `cursor_caps_mode`,
  `request_cursor_updates`, and `InputMethodManager::update_selection`
  to push the selection back — is the full surface an IME needs.
  **This changes what I2 costs**: the IME bridge is a trait to
  implement over iris's parley editor, not a gap to fund upstream. It
  also means E2 inherits Masonry's TODO, so a Masonry transcript will
  have the same dead composer until somebody fills that in.
  
  **Measured on the emulator, same session, same device.** Built
  android-view's own demo — `cargo ndk -t x86_64 -P 26 -o
  app/src/main/jniLibs/ build -p android-view-demo --release`, then
  `./gradlew :app:assembleDebug`, installed with `ANDROID_SERIAL=$(emu
  serial)` — and tapped into its editor. `dumpsys input_method` reports
  `mInputShown=true` with `mServedView=…viewdemo.DemoView`, and the
  screenshot shows **Gboard's suggestion strip populated with "dolor |
  Dolores | door"**: the caret had landed inside the word *dolor* in
  the demo's lorem ipsum, and Gboard read that word out of the Rust
  editor through `text_before_cursor`. So on this emulator, through
  android-view, a parley editor gets a real IME with real suggestions
  drawn from its own buffer. That is the bar E1 could not reach and the
  bar I2 is written against, and it is now known to be reachable.
  
  *One crash seen once — reproduced and diagnosed 2026-09-04.* With an
  accessibility client attached the app aborted, stack:
  `android_view::view::do_frame` → `CallbackCtx::finish` →
  `accesskit_android::event::QueuedEvents::raise` →
  `send_completed_event` → `unwrap()` on `Err(JavaException)`.
  android-view builds `panic = "abort"`, so a JNI call that throws
  takes the process. Two later `ui-trace record` runs left the app
  alive, so the trigger looked narrower than "a client is attached".
  
  **It is the opposite of "a client is attached": it is a client
  having *detached*.** `accesskit_android`'s `State` enum
  (`adapter.rs:161` in 0.4.0, `:192` in 0.8.0) is
  `Inactive | Placeholder | Active`, and **nothing ever moves it back
  to `Inactive`**. A client — `ui-trace`, which is uiautomator — calls
  into the node provider once, `get_or_init_tree` promotes the adapter
  to `Active`, and it stays there for the life of the process. Every
  later change then returns `Some(QueuedEvents)`, `raise` calls
  `ViewParent.requestSendAccessibilityEvent`, and that reaches
  `AccessibilityManager.sendAccessibilityEvent`, which on the main
  looper **throws `IllegalStateException("Accessibility off. Did you
  forget to check that?")` when accessibility is disabled**. jni-rs
  returns `Err(JavaException)`, `send_completed_event` unwraps it, and
  `panic = "abort"` ends the process.
  
  *The controlled run*, one process (pid 4085), `settings get secure
  accessibility_enabled` = 0 throughout:
  
  - tapped the editor and typed three keys with `adb shell input tap`,
    no client ever attached — **alive**;
  - one `ui-trace record -d 800` with no gesture at all, then two
    seconds' wait — **still alive** (the queue was raised while the
    client was still there);
  - the very next three keystrokes, same process — **aborted**, same
    stack.
  
  So the failure is not the recording; it is the **first thing that
  changes the accessibility tree after a recording ends**. That makes
  it a standing hazard for this project rather than an oddity:
  `transcript-bench.sh`, `stream-bench.sh` and `bench-lib.sh`'s
  tap-by-name all attach and detach uiautomator, so on a Rust app the
  typing or scrolling *after* a bench run is what dies, several
  seconds away from anything that looks like a cause.
  
  **Still present at head**: 0.8.0 is the newest `accesskit_android`
  (the demo resolves 0.4.0) and both the unconditional `unwrap` in
  `send_completed_event` and the one-way `State` are unchanged there,
  so upgrading is not the fix. **Our mitigation for I2/I4 is a gate we
  own**: ask `AccessibilityManager.isEnabled()` before calling
  `raise`, and drop the events when it says no. Worth reporting
  upstream as well — the honest fix is for `raise` to clear a pending
  exception rather than unwrap it, since a view can be detached or
  accessibility switched off between queueing and raising no matter
  who is calling.
  
  *A rig trap that cost a wrong conclusion.* Several bounded runs were
  given `sleep N; emu down` watchdogs, and one armed for an earlier
  experiment fired in the middle of a later one — the app vanished, adb
  hung, and it read exactly like the Vulkan path crashing. It was not.
  A watchdog must be scoped to the process it guards (`kill $pid`, with
  the pid captured at launch) rather than to whatever AVD is running
  when it wakes, and only one should be armed at a time.
  

• E2 — a transcript in Masonry. One screen: open a sandbox session, page 800 events into VirtualScroll bottom-anchored, draw markdown from pulldown-cmark into Parley rich text with links and code chips, select across two rows with the platform handles, expand a tool row holding its top edge. Pass: the render numbers land within the Compose baseline in transcript-bench.sh on the GPU emulator (same gestures, same session), and every one of the seven behaviours above is either shown or has a written reason it cannot be.

• E3 — the shell. Kotlin MainActivity + NotificationService + Keystore + share intent calling into Rust over JNI, with the SSE follow loop in Rust. Pass: a notification arrives with the app closed, and a share lands in a session.

• E4 — the same screen on the desktop in a winit window, from the same crate, with only the layout differing.

• E5 — the packaging xtask: cargo ndk → javac/d8 → aapt2 → zipalign → apksigner, signed with the existing release key, installed through Dev Updater. Pass: the APK installs over the Gradle-built one and the notification service starts.

The iris track

These build iris up to carry the app. Each is a feature added to iris with a pass condition, in dependency order. Work in iris/ in this repository on the rustify branch, and record in this file what each step measured.

• I0a — where iris lives (decided 2026-09-04). For now it is vendored at iris/ in this repository, history not carried, and consumed by path. Iris's decision: keep it close while it is being reshaped for this app, and give it back its own repository — iris/iris on the gitea remote, which already holds the full 244-commit history, on a branch of its own — once it has proved itself. The vendored tree is that repository's main at 7b54aaf ("readme", 2026-01-29), byte-identical to the public GitHub copy, so a later reconciliation has a known base. A crate that uses it says iris = { path = "../iris" }.

• I0b — make it build here (done 2026-09-04). iris now builds, clippy-clean and rustfmt-clean at the defaults, on a pinned dated nightly, and the tabs example draws on this VM's GPU.

  **The pin** is `nightly-2026-09-03` (rustc 1.100.0-nightly,
  `2e2b193f8`), declared in `iris/rust-toolchain.toml` along with the
  `clippy`/`rustfmt` components and the two Android targets, so a
  fresh clone provisions itself. It is dated rather than `nightly`
  because the whole failure below was a rolling channel moving under
  an unattended build. Installed with `--profile minimal`: 912 MB.
  
  **The 36 errors were one syntax change, and the earlier diagnosis in
  this file was wrong.** It is not that a trait must now be declared
  `const trait` — the vendored tree already declares them that way,
  which is how it was written in January. What changed is the *impl*
  keyword order: `impl const Trait for T` is now
  `const impl Trait for T`, and generics go on the `impl`
  (`const impl<T: [const] Foo> Bar for T`). Bounds are unaffected;
  `T: const Foo`, `T: [const] Foo` and `impl const Foo` in argument
  position all still compile. Everything else — the unresolved
  `UiVec2`/`Vec2`/`impl_op` imports, and a `Color<u8>` that resolved
  to `wgpu_types::Color` — cascaded from the seven files that failed
  to parse. The rewrite was mechanical across 20 sites and took the
  workspace from 36 errors to 0.
  
  **`#![feature]` gates, 12 after this step** (two were declared and
  unused, and were removed: `map_try_insert`, `const_cmp`).
  Load-bearing and worth watching: `const_trait_impl`, `const_ops`,
  `const_convert`, `const_destruct` are the const-traits family and
  the one that has already broken once — they move together, so
  advancing the pin means re-reading this section. `unboxed_closures`
  + `fn_traits` (postfix builder API) and `unsize` +
  `coerce_unsized` (widget handles) are pairs. The rest are
  individually small: `macro_metavar_expr_concat`, `portable_simd`,
  `associated_type_defaults`, `option_into_flat_iter`, and `gen_blocks`
  in the top crate.
  
  **Running it headless.** `iris/run-headless.sh EXAMPLE [--shot PNG]`
  with `iris/headless.conf`, the same trick `emu` uses: a headless
  sway, and `grim` for the picture. It deliberately starts its *own*
  compositor rather than joining `emu`'s — sway tiles, so adding a
  window to the one an emulator sits in resizes that emulator.
  Unlike `emu`'s it disables Xwayland, since winit speaks Wayland.
  **This VM has a real GPU for this**: Vulkan 1.4 through Venus onto
  the host's RX 7900 XT, and GL 4.6 through virgl — so desktop wgpu
  work here is not software-rasterised, unlike inside the emulator.
  
  **iris has no tests at all** (`cargo test --workspace`: 0 passed
  across 6 targets). Nothing to keep passing, and nothing to catch a
  regression — worth knowing before I1 changes the text stack.
  
  **`iris-core` no longer depends on winit, and now cross-compiles to
  Android.** It wanted exactly one thing from it — `PhysicalSize<u32>`
  in `UiRenderNode::resize`'s signature, for two numbers it immediately
  turned into floats — and that pulled a whole windowing backend into
  the layer below it, the wrong direction. `resize` takes
  `impl Into<Vec2>` now, like `UiRenderState::resize` beside it already
  did. The consequence is the point: with winit in the graph an Android
  build of the core failed in `android-activity` (which needs a backend
  feature nothing here selects), and without it
  `cargo ndk -t arm64-v8a -P 26 build -p iris-core` finishes in 30s and
  produces an rlib, wgpu's Android backend included. So **iris's
  widget, layout and render core already builds for the phone**, and
  what I2 has to supply is the surface, the input and the IME — not a
  port of the library.
  
  **Build weight, cold, on this VM's 8 cores** (`rm -rf target`, then
  `cargo build --example tabs`), since "the Linebender stack is slow in
  debug" was the worry behind this question: plain debug **43s** and a
  2.1 GB `target/`; with the `[profile.dev.package."*"] opt-level = 2`
  knob, **1m46s** and 1.5 GB. So iris's own wgpu + winit + cosmic-text
  graph is not the slow thing — which makes it a calibration for E1
  rather than an answer about Masonry, whose graph adds Vello, Parley,
  Fontique and Skrifa. Runtime cost of the knob was not measured here.
  
  **Fixed: iris never called `pre_present_notify`.** The symptom was
  that about one start in five kept the window's 800x600 startup layout
  on a 1920x1200 surface for good. What settled it was tracing iris's
  own decisions into memory and dumping them from another thread —
  `eprintln!` in the draw path makes the defect vanish, which is why
  earlier attempts kept losing it. The traces from a good and a bad run
  are **byte-identical**: both lay out and draw `redraw_all at
  (1920, 1200)` into a 1920x1200 texture with `suboptimal=false`. iris
  was drawing the right frame every time; the compositor was still
  showing the first one, and forcing a full repaint did not shift it.
  What was missing is winit's `Window::pre_present_notify`, called
  immediately before `present`, which on Wayland is what ties the
  commit to the surface's frame callback. Without it a frame drawn with
  nothing following it can sit unpresented with nothing left to flush
  it — which is exactly a window that has just settled after its
  opening resize. Measured: **0 bad in 40** with the fix, against 4 in
  20 before it, and — the stronger evidence — 0 in 20 in the
  instrumented configuration that had been 15 in 20. Runtime resizing
  still round-trips to a byte-identical layout.
  
  Two things ruled out on the way, both worth not re-trying: the
  present mode (the fault survived the move from `AutoNoVsync` to
  `AutoVsync` at the same rate) and the size cache (`redraw_all` clears
  it). A `desired_maximum_frame_latency` of 1 moved the rate without
  fixing it, and was reverted. Iris's own note that she had never seen
  the library fail to resize was the useful steer: it pointed away from
  the layout code, where two hours had already gone.
  
  One thing was fixed on the way, and it is not that bug: `update`
  redrew everything when `resized` was set, but `needs_redraw` — which
  is what decides whether to *ask* for a frame — did not know about
  `resized` at all. The two now share one `needs_redraw_all`, since a
  condition in one and not the other is a frame nobody requests. It is
  latent on Wayland only because winit asks for a redraw after a resize
  by itself; on Android, where the surface work of I2 will not have
  winit underneath it, nothing else here would have asked.
  

• I1 — parley, and a glyph atlas (done 2026-09-04). No bake-off: Iris decided for parley directly ("I wanted to switch it to parley anyways"), and then asked for the atlas as well ("just do the atlas, commit to it, we do want it"). Both are in.

  **What parley bought, beyond shaping.** Its editing model addresses
  text by byte offset into one string, where cosmic-text used
  `(line, index)` — so `select_content`, `delete_between`,
  `insert_inner` and `newline` collapse into ordinary string
  operations. Bigger: `Selection::geometry` and `Cursor::geometry`
  replace `iter_layout_lines`, `index_x` and `cursor_pos`, which walked
  runs by hand to place the caret and the selection boxes and were not
  bidi- or wrap-correct. `edit.rs` lost about 130 lines and gained
  Home/End. Its cursor motions map onto parley's `next_visual`,
  `previous_visual_word`, `next_line` and so on, in one function.
  
  **The atlas is what "text resizing (per frame) is really slow"
  was.** Every string used to be rasterised into its own `RgbaImage`
  and uploaded as a whole texture whenever anything about it changed,
  so a window resize re-rasterised and re-uploaded every visible
  string. Now a glyph is rasterised once per font, size and subpixel
  phase, shared by every string that contains it, and a resize
  re-emits quads without touching the GPU's copy. **The tabs example
  reports it: `views`, the number of texture views bound, went from 6
  to 1** — six per-string textures became one shared page. Supporting
  pieces: a `GLYPH` primitive that samples a sub-rectangle and tints
  it (the existing texture primitive samples a whole texture), a
  `Patch` texture update so a new glyph costs its own bytes rather
  than a 4 MB page, and `GpuTextures` keeping its `Texture`s, since a
  view cannot be written through.
  
  **Not yet measured**, and the honest gap in this step: the TODO's
  "really slow" was never given a number, so neither is the
  improvement. What is evidence rather than argument is the view count
  and the shape of the work — a resize no longer rasterises. A
  before/after timing wants the transcript screen of I5 to be worth
  taking.
  
  **Two bugs found on the way**, both pre-existing: `primitives!`'s
  `@count` rule recursed comma-separated while matching
  space-separated, so it terminated only for exactly two primitives
  and adding a third hit the recursion limit; and `Color` had no
  `Default`, which parley's `Brush` requires.
  
  **Fourteen tests**, iris's first. The editor is the one part that is
  pure logic rather than something needing a GPU and a window, and it
  was rewritten wholesale with no way to exercise it — synthetic input
  does not reach a client under the headless compositor, which has no
  seat devices. Two of the tests are aimed at what the rewrite could
  plausibly have broken: the IME preedit path, and editing multi-byte
  text now that offsets are bytes.
  
  Dropping cosmic-text and unicode-segmentation also retired two
  nightly gates — `portable_simd` (the old glyph compositing) and
  `gen_blocks` (the deleted line iterator). **Eleven left.**
  

iris's binding array does not survive real Android hardware (found 2026-09-04, resolved 2026-09-04)

Resolved the same day: see "Where things stand" above and TEXTURES.md's "Implemented, 2026-09-04". The measurement and sourcing below are unchanged and are why the fix looks the way it does; nothing here needs re-checking on its own account.

Iris asked, of the "unknown number of images" case — a transcript with an unbounded number of attached screenshots — whether iris's approach even works on a phone, since her recollection was that mobile does not support it. Checked rather than assumed, and the recollection is right, with sources rather than a guess.

What iris does today. Every texture — every Image widget (src/widget/image.rs) and every glyph atlas page — gets its own permanent slot in one array via Textures::add (core/src/primitive/texture.rs:65), and both the TEXTURE and GLYPH primitives sample it by view_idx into binding_array<texture_2d<f32>> at core/src/render/shader.wgsl:56, sized by UiLimits::default — 100,000 textures, 1,000 samplers (core/src/render/mod.rs:347). That needs three wgpu features: TEXTURE_BINDING_ARRAY, SAMPLED_TEXTURE_AND_STORAGE_BUFFER_ARRAY_NON_UNIFORM_INDEXING, PARTIALLY_BOUND_BINDING_ARRAY — Vulkan's VK_EXT_descriptor_indexing ("bindless"), promoted to core in 1.2. So a transcript with an unbounded number of images is exactly the case that grows this array without bound, one permanent slot per image.

Measured first on the emulator, and it fails outright. A rig (rigs/gpu-probe, a plain executable with no window, pushed with adb push and run from /data/local/tmp — no APK needed to ask a device what it supports) asks wgpu::Adapter::request_device for exactly iris's features and limits. Against the emulator's guest Vulkan — both SwiftShader (vk_swiftshader_icd.json) and lavapipe (lvp_icd.json, cold-booted) — request_device fails: Unsupported features were requested: TEXTURE_BINDING_ARRAY | SAMPLED_TEXTURE_AND_STORAGE_BUFFER_ARRAY_NON_UNIFORM_INDEXING | PARTIALLY_BOUND_BINDING_ARRAY. A second, raw query through ash (rigs/gpu-probe/src/vk.rs, bypassing wgpu) shows lavapipe's vkGetPhysicalDeviceFeatures2 actually reporting all seven descriptor- indexing sub-features as true at device api version 1.3 — so on this software renderer wgpu-hal's own feature detection is being more conservative than the driver, for a reason not chased further (a likely instance-version negotiation gap, since VK_EXT_descriptor_indexing was only promoted to core at 1.2 and wgpu-hal's own Instance::init may be requesting less). That part is an emulator/wgpu-hal question and not the finding that matters.

The finding that matters is about real phones, not the emulator, and it is sourced rather than recalled. The Android Vulkan Profile 2025 — Google and Khronos's current baseline, covering 80.1% of active Vulkan-capable Android devices as of October 2025 (developer.android.com/ndk/guides/graphics/android-vulkan-profile) — does not require VK_EXT_descriptor_indexing or any descriptor- indexing feature. It requires shaderSampledImageArrayDynamicIndexing (indexing an array of samplers by a value uniform across the invocation — Vulkan 1.0 baseline, unrelated to bindless) and stops there; the same is true of the 2021 and 2022 profiles. On the hardware side, Arm's own developer documentation states "VK_EXT_descriptor_indexing is supported on all Valhall and 5th Gen GPUs" (developer.arm.com/mobile-graphics-and-gaming/vulkan-api-best-practices-on-arm-gpus) — Mali generations from roughly 2019 (Mali-G77) onward, named affirmatively with no claim made for Bifrost, Midgard or Utgard, which are still common in budget and older Android phones still in use. So this is not a software-renderer artifact: a real, currently-shipping share of the Android fleet lacks the feature iris's texture pipeline asks for unconditionally, and the newest official baseline does not promise it either. (A crates.io/search-engine claim of "1% support on Android" for this extension was checked against its cited source, an Arm blog post, and was not actually there — that number does not appear anywhere primary and should not be repeated; the 80.1%-baseline-excludes-it finding above is the one with an attributable source.)

Recommendation, not yet implemented. iris already solved the identical problem for text in I1: the glyph atlas (core/src/render/atlas.rs) packs many small rasters into a handful of shared 1024×1024 pages and samples them by UV offset, so text needs none of the three features above — only ordinary single-texture sampling. The same technique generalizes to images: route an Image widget through a shared atlas when it is small enough to pack (thumbnails, downscaled attachment previews, avatars, icons), and fall back to one ordinary, non-array texture bind group — selected per batched draw call the way every immediate-mode 2D renderer already does — for anything too large to atlas well (a photo opened at full resolution). Either path is plain Vulkan 1.0 / GLES texture sampling, so it removes the descriptor- indexing requirement from iris's device request entirely, which is also what would make the emulator work regardless of the wgpu-hal question above: a device that never asks for the feature cannot be refused for lacking it. This is a change to iris's rendering core — the shader's binding group layout, Textures, the texture and glyph primitives, and ui/painter.rs — so it is written here as a recommendation rather than started, per the project's rule to confirm a load-bearing design change before making it. It should be resolved before I2 is called done, since I2's pass condition is the phone, not just the emulator, and this is exactly the kind of thing that passes on a desktop GPU and fails silently on real hardware.

• I2 — iris on android-view (2026-09-05). The android-view backend, the iris-android-app cdylib and Gradle shell, insets, the back gesture and the full InputConnection bridge are in and measured working; the tabs example now renders on the emulator (Vulkan/ SwiftShader and GLES/virgl both), and the composer's keyboard shows real Gboard suggestions through the IME bridge. See below for the render-gap root cause and fix.

  **Layout.** `iris/src/android/` mirrors `default/`'s module split
  (`view.rs` is `app.rs`+`state.rs` combined, since android-view has one
  harness type where winit splits `ApplicationHandler` from per-window
  state; `render.rs`, `input.rs`, `attr.rs` correspond directly;
  `ime.rs` and `insets.rs` have no winit counterpart). What used to live
  only in `default/` and had no winit dependency — `WidgetState`,
  `CursorState`/the sense machinery, `Tasks`, `Selector`/`Selectable`'s
  focus handling — moved to crate-root modules (`state.rs`, `sense.rs`,
  `task.rs`, `attr.rs`) so both backends use one copy; `Tasks`' redraw
  nudge is now behind a `RequestRedraw` trait (`Window` for winit, a
  `JavaVM`+`GlobalRef` attach-and-call for android-view) rather than a
  concrete `winit::window::Window`. `winit`/`arboard` and
  `android-view`/`send_wrapper` are now `[target.'cfg(...)']`
  dependencies, and `default`/`android` are target-gated modules,
  because winit's own Android support needs `android-activity` with a
  backend feature selected — exactly what `iris-core` was kept free of.
  Confirmed by trying it before the split (`cargo ndk -t x86_64 -P 26
  build -p iris` failed inside `android-activity` itself) and after
  (clean). `iris/tabs-ui` is the tabs example's widget tree factored out
  of `examples/tabs/main.rs` into a crate generic over `Rsc: HasEvents`
  + `Rsc::State: FocusHost`, so the winit example and
  `iris/android-app` (the new cdylib, excluded from the `iris` workspace
  because android-view needs the NDK sysroot to link — see that
  `Cargo.toml`'s comment) call the same `build()`.
  
  android-view pinned to `bec6c62a96cef8239b0fd7fedeef9b184d02e3a1`, the
  commit E1 measured against. `RustView.java`/`RustInputConnection.java`
  are vendored (no published AAR to depend on) into
  `iris/android-app/app/src/.../org/linebender/android/rustview/`, with
  one deliberate diff from upstream noted in a comment: `mViewPeer` is
  `protected` rather than package-private, so `IrisView` (a different
  package) can pass it to the window-insets native call android-view
  has no hook for.
  
  **Insets and the back gesture**, both without touching android-view.
  The back gesture takes no new plumbing at all: with no
  `OnBackPressedCallback` registered, Android still delivers it as an
  ordinary `KEYCODE_BACK` `KeyEvent` through the existing key path (the
  legacy behaviour every view-based app gets by default), handled in
  `view.rs`'s `on_key_down`. Insets have no such stand-in, so
  `android/insets.rs` registers one more native method
  (`applyWindowInsetsNative`) directly on `IrisView`, writing into an
  `Rc<RefCell<Shared>>` a second copy of which lives in
  `AndroidUiState` — the peer id android-view hands back from
  `register_view_peer` is opaque outside that crate, so this is a
  side table keyed on the same id rather than a way to reach the peer
  itself. `MainActivity` wires `setOnApplyWindowInsetsListener`,
  including the API 30+ `ime()` inset specifically (falls back to 0
  below that). Not yet consumed by any widget's layout — `insets()` is
  exposed on `AndroidUiState` but nothing reads it yet, since the tabs
  example has no chrome that needs to avoid the keyboard.
  
  **The IME bridge is implemented and its pass condition holds.**
  `android/ime.rs` implements the full `InputConnection` trait
  (`text_before_cursor`/`after_cursor`/`selected_text`,
  `cursor_caps_mode`, `delete_surrounding_text[_in_code_points]`,
  `set_composing_text`/`_region`, `finish_composing_text`,
  `set_selection`, `begin`/`end_batch_edit`, `send_key_event`,
  `request_cursor_updates`) directly against `TextEdit` — the same
  preedit-replace bookkeeping `default`'s `Ime::Preedit` handling uses
  (`compose_len`, in chars), with new byte<->UTF-16 conversion helpers
  since parley (since I1) is byte-indexed and Java strings are not.
  Two approximations, both commented in place rather than silently
  dropped: `set_composing_region` declines (no separate composing range
  exists to move) and `set_selection`/`delete_surrounding_text_in_code_points`
  collapse to an approximation rather than a real span/code-point
  count. `TextEdit` gained `text()`/`selection_range()`/`caret()`
  getters and `TextEditCtx::delete_byte_range`/`set_cursor_byte`, all
  unconditional (no winit dependency added); `apply_event`/
  `TextInputResult`, which do take a `winit::event::KeyEvent`, are now
  `#[cfg(not(target_os = "android"))]` instead of being ported, since
  android's own `input.rs` calls `TextEdit`'s primitives
  (`backspace`/`delete`/`motion`/`insert`) directly from
  `ndk::event::Keycode` and never needed a winit `KeyEvent` shape.
  
  **Measured on the emulator, 2026-09-05, x86_64 API 26,
  `-feature Vulkan` + SwiftShader per the Vulkan section below.**
  `adb shell dumpsys input_method` after tapping the composer field:
  `mInputShown=true`, `mServedInputConnection` is
  `org.linebender.android.rustview.RustInputConnection` attached to
  `IrisView`. `adb shell input text "hi"` followed by a screenshot
  shows **Gboard's suggestion strip populated with "hi | Hi | HI"** —
  capitalization variants read back out of the real buffer through
  `text_before_cursor`, the same kind of evidence E1 recorded (there:
  "dolor | Dolores | door"). That is the bar this box asks for, met.
  
  **Resolved 2026-09-05: the render gap was the window uniform, never
  the atlas.** `UiRenderNode::new` (`core/src/render/mod.rs`) seeded the
  GPU's `window_buffer` from `WindowUniform::default()` — width=0,
  height=0 — and the only thing that ever corrected it was a later call
  to `UiRenderNode::resize`, renamed `AndroidRenderer::resize` on the
  android side. winit's backend gets away with the same default because
  winit fires an initial `WindowEvent::Resized` before the first frame,
  which `default/mod.rs`'s event loop turns straight into that resize
  call — a real event this project never had to add on purpose, so
  nothing here noticed the node depended on it. android-view has no such
  automatic event: `surface_changed` (`src/android/view.rs:363-388`)
  only calls `self.render.resize(...)`, which is
  `UiRenderState::resize` — the CPU-side *layout* width the widget tree
  lays out against — not `AndroidRenderer::resize`, which is the one
  that writes the GPU uniform. `AndroidRenderer::new` builds a fresh
  `UiRenderNode` with the correct `SurfaceConfiguration` (so the surface
  itself was always the right size, and the clear colour reached it) but
  that node's window buffer was never subsequently written, so it sat at
  `(0, 0)` for the node's entire life. `shader.wgsl`'s `vs_main` divides
  by `window.dim` to reach clip space
  (`let pos = (top_left + uv * size) / window.dim * 2.0 - 1.0;`), so
  every primitive's clip position came out `NaN`/`Inf` and was dropped
  before rasterization on **both** backends — Vulkan and GLES alike,
  exactly the cross-backend symmetry that should have pointed away from
  a GL-specific cause sooner. The layout engine reporting the correct
  widget count and pixel region the whole time is consistent with this:
  that path never touches `window.dim` at all, since it is a separate
  copy of the window size (`UiRenderState`'s own, fed by
  `self.render.resize`) that the CPU-side layout and hit-testing use.
  
  **The GLES `D2`/`D2Array` warning was confirmed a red herring.**
  Reproduced again after the fix, unchanged, on a build forced to
  `Backends::GL` — it fires on every frame regardless, and primitives
  draw correctly on that backend anyway (screenshot below), so it is a
  cosmetic wgpu-hal heuristic notice, not a correctness bug in the atlas
  path. Left as-is; chasing it further is not warranted.
  
  **Fix** (`core/src/render/mod.rs`, `UiRenderNode::new`): seed
  `WindowUniform` from `config.width`/`config.height` — already the
  surface's real size at construction time on both backends — instead
  of `WindowUniform::default()`. This removes the dependency on an
  external resize call entirely (winit's initial `Resized` event still
  fires and still calls `resize()`, now idempotently) rather than
  papering over android-view's missing event with one more call in the
  android-specific path; a future third backend gets a correct window
  buffer from its first frame with no equivalent event of its own to
  remember.
  
  **Verified on the emulator, 2026-09-05, `ai-app-2`'s own AVD, x86_64
  API 26, `-feature Vulkan` + SwiftShader per the Vulkan section.**
  `logcat` after launch: `render(): after update active=39
  root_px=Some(PixelRegion { top_left: (0, 0), bot_right: (1080,
  2219) })`, no wgpu validation warnings on the Vulkan build. Screenshot
  (`/tmp/iris_i2_render.png`) shows the tabs example's coloured spans,
  the red rounded rect and the tab bar all drawn — the milestone this
  section asked for. Rebuilt with `Backends::GL` forced (reverted
  afterwards; the shipped code still requests `Backends::PRIMARY`) and
  reinstalled: same screenshot, same widgets, `AdapterInfo` logged as
  `Android Emulator OpenGL ES Translator (virgl (AMD Radeon RX 7900
  XT...` confirming the real GLES/virgl path, with the `D2`/`D2Array`
  warning present and harmless as above. Text glyphs render with visible
  artifacting on the GLES path specifically (not investigated further —
  out of scope for this box, which is about primitives appearing at
  all, and it does not affect the Vulkan path this app ships behind).
  
  **Not built yet**: anything consuming `insets()`, a real phone
  measurement (only the emulator so far — matches every other Android
  finding in this file), and AccessKit (I4's job, so `ui-trace`
  couldn't be used here; a raw `adb shell input tap`/`input text` stood
  in for driving the UI, which is why this section says "the same bar
  as E1" rather than citing a `ui-trace` transcript).
  
  **Verification.** Host: `cargo fmt --all -- --check`,
  `cargo build --workspace --all-targets`, `cargo clippy --all-targets`,
  `cargo test --workspace` (19 tests) all clean in `iris/`; `iris/run-headless.sh
  tabs --shot` still renders pixel-identically (27266 bytes, byte-for-byte
  unchanged). Android cross-compile: `cargo ndk -t x86_64 -P 26 build`
  and `... clippy` clean for both `iris` (with the android module) and
  `iris/android-app`. Emulator: `emu up` with
  `VK_DRIVER_FILES=.../vk_swiftshader_icd.json` and
  `GPU_HOST_FEATURES="-feature Vulkan -no-snapshot-load -no-snapshot-save"`
  per the Vulkan section; `cd android-app && cargo ndk -t x86_64 -P 26
  -o app/src/main/jniLibs/ build --release && gradle :app:assembleDebug`
  (release native lib per E1's segfault finding, debug Gradle variant --
  the jniLibs contents are what matters, not the Gradle build type);
  `adb install -r app/build/outputs/apk/debug/app-debug.apk`. Emulator
  torn down after verification (`emu down`) per the machine's memory
  rule.
  

• I3 — a virtualised, bottom-anchored list. Variable-height rows, keyed, composed only while visible, paged in both directions with a "more" sentinel at each end, a scroll anchor that survives rows being inserted above, and "hold the edge nearest the tap" done in the layout pass. Pass: 800 rows of real transcript text from the sandbox scroll without a frame over the Compose baseline in transcript-bench.sh, measured on the GPU emulator.

• I4 — accessibility names via AccessKit. Every control carries a name; ui-trace can find and tap it by label. Pass: bench-lib.sh's tap-by-name works against the iris screen unchanged.

• I5 — the transcript screen in iris. E2's pass conditions, all seven behaviours, against the sandbox with --delay. This is the point the decision in the recommendation is made at.

For the next agent

What to do when you pick this up, in order, so nothing here has to be re-derived:

1. Read this file, then AGENTS.md and PLAN.md. The rules there (measure, do not read; fix the rig before accepting its limits; the emulator is this checkout's own) all apply.
2. Work on the rustify branch of this clone (ai-app-2), not on main and not in ai-app. Nothing on this branch is production until Iris says so. Commit and push as you go.
3. Take the next unchecked box above, in order. E1 has proved android-view on this emulator, so the E-steps and the I-steps can now proceed in parallel in separate sessions; see "Where things stand" at the top for which is next.
4. Every step ends with its measurement written into this file beside the box, and the box ticked or the reason it could not be written in its place. A step that is blocked says by what, not "later". Write it as you go rather than at the end — see "Keep this file current as you work".
5. Run the existing rigs rather than inventing new ones: ui-sandbox.sh for a server with fixtures, transcript-bench.sh for the scroll baseline, ui-trace for anything positional, emu up for the emulator, iris/run-headless.sh EXAMPLE --shot PNG for an iris example on this displayless machine, and rigs/gpu-probe to ask a device (this VM, the emulator, or a real phone over adb push) what wgpu features and limits it actually has before building anything on the assumption it does. The Vulkan section below says how to get a Vulkan path in the emulator when a wgpu backend needs one.
6. Bound anything heavy at the moment you start it. An emulator or a long build gets a deadline — timeout, or a watchdog scoped to the pid you just started — rather than a plan to stop it later. Scope it to that pid: a watchdog written as sleep N; emu down fired into a later experiment here and made a working Vulkan build look like a crash. And stop the emulator when the work needing it is done rather than between tasks.
7. Decisions belong here with a date and what was rejected, the way PLAN.md does it. Do not put design into commit messages alone.

Vulkan in the emulator (measured 2026-09-04)

Settled 2026-09-04: the guest gets Vulkan from SwiftShader, and the missing step was a cold boot. -feature Vulkan plus VK_DRIVER_FILES=$HOME/Android/Sdk/emulator/lib64/vulkan/vk_swiftshader_icd.json gets the host side to select SwiftShader, but the guest keeps reporting zero devices until -no-snapshot-load is added, because it boots from a snapshot saved under the previous GPU config — -no-snapshot-save is worth adding too, so the Vulkan-configured snapshot does not then break the next ordinary boot. With that, cmd gpu vkjson reports SwiftShader Subzero and wgpu takes its Vulkan path (E1). EMU_GPU=software in emulator-tools gets the same guest Vulkan with no GPU use at all, for work where the emulator's frame rate is not what is being measured.

The rest of this section stands as the record of why host Vulkan is not available. A wgpu app in this emulator was going to get GLES only, because host Vulkan is switched off in emulator-tools. Retried on Mesa 26.1.7: Venus still fails the same way — gfxstream picks externalMemoryMode: OpaqueFd, probes VK_FORMAT_R8G8B8A8_UNORM for an exportable colour buffer, and Venus says the format is unsupported (Failed to find memory type for ColorBuffers, fatal before adb sees the device). Venus does advertise VK_KHR_external_memory_fd and VK_EXT_external_memory_dma_buf, so the gap is specifically opaque-fd image export. gfxstream has a string-valued VulkanExternalMemoryMode setting ("overrides what would otherwise be determined automatically"), but -feature Name=Value is rejected as a bad feature name, and the only mode words compiled into this emulator's libgfxstream_backend.so (37.1.11) are OpaqueFd, Metal and none — there is no dma-buf mode in this build to switch to. So Venus is blocked by the emulator, not by Mesa; retry when the emulator package updates, since upstream gfxstream does have dma-buf external memory.

What does work: pointing the emulator's Vulkan loader at the software ICDs the emulator ships itself, with the feature enabled:

VK_DRIVER_FILES=$HOME/Android/Sdk/emulator/lib64/vulkan/vk_swiftshader_icd.json \
GPU_HOST_FEATURES="-feature Vulkan" emu up

The guest then reports Vulkan 1.3 (cmd gpu vkjson, SwiftShader Subzero) while GLES still runs on the real GPU through virgl — so a Vello/wgpu app can take its real Vulkan path here, with compute shaders, CPU-rasterised. That is enough to test correctness of the Vulkan path in the emulator; GPU performance of it is a phone measurement either way, exactly as MACHINE.md already says about frame times. lavapipe (lvp_icd.json, the other ICD the emulator ships) selected llvmpipe and booted, then the emulator died right after loading the default_boot snapshot with nothing in the log; a snapshot saved under a different Vulkan device is the suspect, and -no-snapshot-load is the untested next step. SwiftShader is the one that works today. EMU_GPU=software is now in emulator-tools (agreed with the ai-app session and with Iris, default unchanged, since -gpu host was measured and the Compose scroll benchmarks depend on it). The cold-boot flags are not a knob there: that wants snapshot invalidation as well, which is a bigger design question in shared tooling.

Things a Rust app changes elsewhere

• wg-app-link's :link (pinned TLS, enrollment store, QR activity) is Kotlin shared with Dev Updater. The certificate code already exists on the Rust side of the submodule; the pinned-CA build step (generatePinnedCert) becomes a build.rs reading the same path. The QR scanner stays a Kotlin activity, since the camera is a platform feature.
• Tooling becomes cargo for everything but packaging: cargo test, clippy, fmt cover the whole client, which is the motivation. Gradle remains for the APK, signing (~/.config/ai-app/release.jks) and Dev Updater's build modes; build-apk.sh would call cargo ndk first.
• The bench scripts (ui-trace by accessibility label) keep working only if the framework exposes names through AccessKit on Android; that is part of E2's pass condition, not a nicety.
• Icons stay Nerd Font glyphs from the committed subset; Parley/Fontique loads a font file directly, so build-icon-font.sh is unchanged.

Sources

• iced: repo, 0.14 release, Android thread, markdown selection request
• Linebender: 2026 Q1 report, xilem, parley, vello, vello_hybrid
• android-view: repo; android-activity PR #214
• winit Android IME: #1823, #2766, #2305
• egui on Android: discussion #2053
• Slint: Android guide, 1.15 release, licensing, rich text #1325, markdown #6684
• Makepad: repo, makepad-widgets, Robrix, Robrix releases
• AccessKit: releases
• Build tools: cargo-ndk, cargo-apk, rust-mobile
• uniffi: repo, KMP bindings fork
• GPUI mobile: gpui-mobile
• The earlier Dioxus spike's findings on wgpu/Vulkan in this emulator: ~/repos/tdep-survey/app-dioxus/README.md