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

- **P0's Compose half is built and smoke-tested on the emulator** — the
  `bench` build type, the shared `app/bench-fixture/` transcript, and an
  in-process fake backend (`BenchFixture.kt`/`BenchNetwork.kt`) that
  answers `TranscriptSource`/`EventStream` from an in-memory event log
  instead of a real server, so the fold and paging under test are the real
  ones. Full account, the smoke run's report, and what is deliberately
  left (the iris half, the real on-phone runs) are in RUST.md's P0 box.
  Not a decision to review so much as the gate itself now being runnable —
  flagged here because it is the first half of something Iris explicitly
  asked to see before P1.

- **The intermittent touch-scroll dropout is root-caused and fixed: a
  missed `ACTION_DOWN` hit-test, not the previously-suspected coalesced
  first `ACTION_MOVE`.** Diagnosed by temporary logcat tracing of every
  touch event, `DragArbiter` state transition and `Selection::drag`
  dispatch (removed once confirmed), reproduced on this checkout's own
  emulator against a real sandbox session. The trace showed the actual
  mechanism: a gesture's `ACTION_DOWN` lands wherever the finger actually
  is, which is not guaranteed to fall inside the same row-local sensor
  region a later `ACTION_MOVE` in the same gesture lands in (a row's own
  padding/gap, or its non-selectable sender-name header, is
  pointer-transparent to `iris::sense::CursorSense`). When that happens,
  the widget that ends up handling the gesture never saw `PressStart`, so
  `DragArbiter` sits in `Idle` — which answers every subsequent frame with
  `Undecided` and has no way to tell "no press is happening" from "a press
  is happening but I missed its start," so it never recovers on its own
  for the rest of that gesture. One real trace showed exactly this: touch
  `Down`/`Move`/`Up` all delivered correctly, but zero `PressStart`
  reaching the arbiter, `state=Idle` unchanged from first frame to last.
  Fixed at the call site that has the context to recover
  (`iris::transcript_ui::selection::Selection::drag`,
  `iris/transcript-ui/src/selection.rs`): a new `DragArbiter::is_idle()`
  (`iris/src/sense.rs`) lets it notice a `Pressing` frame arriving with the
  arbiter still `Idle` — which can only mean a missed `PressStart`, since a
  `Pressing` sense requires the button to genuinely be down — and start the
  press there instead of where it was missed. Three new unit tests in
  `sense.rs`'s `drag_arbiter_tests` and one in `transcript-ui`'s
  `selection::tests` (the latter fails on the code before this fix).
  Commit follows. Not the same failure the earlier pass's `DECISIONS.md`
  DEFERRED item speculated about (a coalesced first `ACTION_MOVE` skipping
  slop detection) — that hypothesis is now ruled out; the arbiter's own
  slop/long-press logic was never wrong. RUST.md's I5 box,
  "Touch-scroll dropout root-caused, 2026-09-05" has the full trace.
- **P0, a phone benchmark gate before any porting, asked for by Iris
  2026-09-05**: "before P1 I'd like to see benchmarks & also maybe stress
  test on my own phone ... If it doesn't match compose reasonably well then
  I don't think I'd wanna continue." Design (RUST.md's P0 box has the
  detail): the same embedded synthetic fixture in both apps with no server
  needed; the same scripted scroll loop then a streaming phase, run
  programmatically since the phone has no usable system tracing and no
  agent can drive it; the same report from both (frames, janky %, p50/p90/
  p99, process CPU time, peak RSS, battery current where readable) with a
  copy button; the iris app under its own id and the Compose one as a new
  `bench` build type with an id suffix, so neither replaces her production
  install; two arm64 APKs plus instructions delivered under `~/host/bench/`.
  The gate is hers: iris within a reasonable margin of Compose release on
  p50, p99 and CPU time, no crashes, no visible stutter. If it fails, the
  port stops.
- **The rest of the port is one UI crate, `iris/app-ui`, grown out of
  `iris/transcript-ui` rather than started beside it.** It holds a
  `Screen` enum plus a back stack — the Rust equivalent of `AppRoot.kt`'s
  `when` — and `iris/desktop-app`/`iris/android-app` become thin entry
  points over it. Chosen over a fresh crate because `transcript-ui`
  already has the right generic shape (`Rsc: HasEvents` +
  `Rsc::State: FocusHost`) and the `client-core`/`event-model` path
  dependencies every later screen needs, so growing it in place is the
  smaller diff. Platform-only code (notification service, share target,
  QR scanner, Keystore token, deep-link enrolment) stays in the E3/E5
  Java shell (`android-shell/` + `app/shellApp`) rather than moving into
  this crate, since none of it is a screen. The Android APK is built by
  `cargo xtask apk` (E5), merging the app-ui cdylib into the E3 shell so
  there is one app rather than a demo shell plus a service shell.
  `app/androidApp` (the Compose app) stays untouched and is the baseline
  every step is measured against, until parity is reached (P7 decides
  the switch, and is itself a load-bearing decision left to Iris). Order
  is by risk to the daily-use path: session screen first (P1, where
  every hard behaviour already lives), then the shell merge and a real
  phone install (P2), then root tabs (P3), the explorer (P4),
  settings/enrolment (P5), desktop parity (P6), and the cutover itself
  (P7). Full plan: RUST.md's "The port, in order (decided 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.
- **DECIDED by Iris, 2026-09-05: iris is the app's framework; Masonry was
  the calibration.** Her words: "I think iris definitely makes more sense
  based on the limitations we've found." The limitations: Masonry has no
  touch scroll on Android (E2), no per-span rich text and no cross-row
  selection on the pinned commit (E2), and its keyboard bridge is a TODO
  (E1); iris carries the same screen under the Compose baseline on the
  host GPU (p50 15.0 ms against Compose's 20.0 ms, RUST.md's I5 box). What
  follows: the E-steps are closed as calibration, and the port proceeds
  on iris — screens, the shell (E3/E5), and `client-core` underneath.
  The item below is kept as the record of what she decided from.
- **Was 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 `SIGSEGV`s 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.