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 `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.