ai-app/docs/DECISIONS.md

Decisions taken for Iris to review

Short list of design choices made by the design agent without asking, so they can be judged and reversed later. Detail lives in RUST.md (and IRIS.md for iris API changes); this file is only the summary. Newest first. Items marked DEFERRED are ones the agent chose not to decide alone.

2026-09-05

• iris gets its own measured frame report, rather than waiting on a dumpsys/gfxinfo answer that cannot see a SurfaceView's GPU-drawn frames. iris_core::FrameReport (iris/core/src/render/frame_report.rs) times each frame's wall clock from the same point render()'s redraw starts to just after queue.submit + present() — the span Compose's own render report and gfxinfo both count — into a fixed 4096-entry ring (no allocation per frame; report() is the only place that allocates, and only on a button tap). The report gives total frames, janky % over the same 16.7ms budget gfxinfo uses, P50/P90/P99 and the worst, plus a reset. Exposed the way the Compose app's copy-button report already is: two named controls ("Frame report", "Reset frame report") on the transcript screen, tappable by accessibility name via ui-trace, logging under this crate's fixed android_logger tag (iris-android-app) so a script can grep "iris frame report" the way transcript-bench.sh greps "ai-app render report". The report's own Display line says plainly that it measures up to the present() call returning, not GPU/compositor completion — wgpu's present() is not fenced against either, so presenting that span as "time to reach the screen" would be a measured-looking number that is actually inferred, which the standing UI rule forbids.

• ui-trace gains a hold-then-drag gesture, additive, in emulator-tools. Neither of its two existing actions can produce "hold stationary for LONG_PRESS, then move without lifting" — tap has no hold and swipe X1 Y1 X2 Y2 MS interpolates motion across its whole duration from t=0. A new action presses, waits, then moves to a second point and releases as one continuous touch (raw sendevent/MotionEvent injection, extending whatever mechanism the existing swipe already uses), so DragArbiter's pan-vs-select rule (iris/src/sense.rs, already covered by 8 unit tests against a synthetic clock) can finally be driven on a real device instead of only in a test harness.

• Touch drag on a transcript row follows Android's own rule: a vertical drag pans the list immediately; a stationary press held 500 ms starts a text selection which further dragging extends; a horizontal drag while something is already selected extends that selection without the wait. One DragArbiter per list decides it (iris/src/sense.rs). Chosen over a "text layer always wins" or "list always wins" rule because either loses one of the two gestures a reader expects.

• E4's desktop shape is a new iris/desktop-app crate: a winit window holding transcript-ui's screen beside a session list, talking to a real ai-server through client-core. It enrols by pasting the same aiapp://enroll?… link a phone scans (client-core::config::EnrolledServer) and keeps it owner-only under $XDG_CONFIG_HOME/ai-app-desktop/. The pinned CA is a path given on the command line, not baked in. Chosen so the phone and desktop share one enrolment format and no second one is invented.

• I5's Android integration extends iris-android-app (I2's shell) behind a Cargo feature (transcript-screen), rather than a third shell crate. That project already has the Gradle module, the IrisView/MainActivity Java, and the JNI registration; the only thing a second screen needs on top is a different AndroidAppState, the same axis tabs_ui::build/transcript_ui::build already vary along on the winit side. tabs-screen/transcript-screen are mutually exclusive and each pulls in only its own deps, so the plain tabs build (I2/I4) is untouched.

• Order of remaining work, updated 2026-09-05: the two in-flight pieces and I5's Android integration are all done; next is giving iris its own frame-timing report so item 3 below can be decided by a number.

• DEFERRED — whether to commit to iris over Masonry for ai-app. Updated 2026-09-05 with the clean comparison the recommendation wanted: same sandbox session content, same emulator, EMU_GPU=software, one session. Headline numbers (RUST.md's I5 box, "Clean scroll comparison, 2026-09-05," has the full table and every caveat):

  app	build	frames	janky %	p50	p90	p99	worst
  Compose (in-app report)	debug	1102	99.0% late	33.8ms	50.6ms	79.5ms	--
  Compose (dumpsys gfxinfo)	debug	1499	21.15% (95.66% legacy)	32ms	48ms	150ms (p99)	--
  iris (FrameReport)	release	299	94.65%	79.1ms	98.6ms	117.8ms	212.6ms
  iris (FrameReport, repeat)	release	233	94.42%	109.3ms	130.8ms	147.1ms	150.5ms

  Not a clean apples-to-apples reading, stated plainly rather than smoothed over: iris had to be built release (debug SIGSEGVs on this emulator's Vulkan loader, I4's finding) against Compose's mandated debug build, so this asymmetry likely understates iris's gap rather than the reverse; the three frame-time sources measure different things (Compose's own phase accounting vs. Android's HWUI deadline-miss definition vs. iris's redraw-start-to-present window, the last of which dumpsys gfxinfo cannot see at all for iris's SurfaceView); and both figures are emulator numbers under software rasterisation, which Compose's own in-app report shows already costs 20-34ms/frame in swap+gpu alone under this GPU mode, so a same-mode iris number well above 16.7ms was expected going in for either app. A second pair under -gpu host was not taken this pass. The earlier session's suspected intermittent touch-delivery dropout was not reproduced this pass — the zero-frame results this time traced to this pass's own script bug (a cd that changed which emulator ui-trace targeted), not the emulator; a CPU-load rise during the gesture was observed by a sampler running throughout, but did not correlate with any failure, so the original candidate is neither confirmed nor ruled out. The choice in front of Iris, updated: decide now on the structural-plus-functional case already made (iris works end-to-end where Masonry's scroll gesture doesn't exist at all on Android) plus this table — reading the two build profiles and three jank definitions with the caveats above rather than as a single number — or ask for a same-profile, same-GPU-mode rerun first. RUST.md's I5 box has the full account.

  Updated 2026-09-05, the -gpu host pair taken. Real GPU rendering (force-gles -- the default Vulkan backend has no adapter at all under plain host-GPU boot, confirmed by the exact wgpu error) reverses the software-mode shape:

  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

  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 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 proof of it: a same-mode software force-gles run to isolate the backend crashed for an unrelated reason (SwiftShader's GL path reports itself as OpenGL ES 3.0, which has no compute shaders, and iris's device request assumes them unconditionally) — real scope to fix, not done here — and the two apps' frame populations still differ in kind the same way the software-mode caveats describe. A real intermittent touch- scroll dropout was also reproduced this pass (six consecutive swipes produced zero redraws while taps kept working; an identical retry then succeeded) and is not explained. RUST.md's I5 box, "Where iris's frame time goes, 2026-09-05, the -gpu host pass," has the full account. The iris-vs-Masonry choice itself is still Iris's to make.