RUST.md, DECISIONS.md: P0, the phone benchmark gate Iris asked for before P1

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/RUST.md

@@ -3238,6 +3238,39 @@ AVD, `ui-trace` by accessibility name, GrapheneOS phone quirks, the
 running any pass condition below that touches an emulator or a real
 device.
 
+- [ ] **P0 — the phone benchmark gate (asked for 2026-09-05; must pass
+      before P1 starts).** Iris runs both apps on her own phone and pastes
+      the reports back; the emulator's numbers are not a substitute.
+      Two halves, buildable independently:
+      - **Compose half** (`app/`): a `bench` build type (release
+        optimisations, `applicationIdSuffix ".bench"`, own label "AI
+        Sessions bench") whose session screen can open an embedded fixture
+        transcript from assets with no server, and a "Run benchmark"
+        control in the existing render-report place that programmatically
+        performs the fixed scroll loop (same distances and timings as
+        `transcript-bench.sh`, driven through the `LazyListState`), then a
+        streaming phase (append fixture events at 20/s for 20 s into the
+        same fold path a live SSE reply uses), then shows the report with
+        the existing copy button. The report adds process CPU time over
+        the run (`Process.getElapsedCpuTime`), peak RSS, and
+        `BatteryManager.BATTERY_PROPERTY_CURRENT_NOW` samples.
+      - **iris half** (`iris/android-app`, `transcript-screen` feature): the
+        same fixture embedded, the same scripted loop and streaming phase
+        driven through `List::scroll` and the fold, the same report fields
+        added to `FrameReport`'s line, shown on screen with a copy-to-
+        clipboard control (through the shell's Java side), arm64 release.
+      - **The fixture**: one synthetic transcript generated from
+        `app/ui-sandbox.sh`'s invented sessions (never a real one), at
+        least 3,000 events, with headings, code fences, links, tool calls
+        with kilobyte outputs, and a few images; committed once under
+        `app/bench-fixture/` and read by both apps.
+      - **Delivery**: `~/host/bench/` gets `iris-bench-arm64.apk`,
+        `compose-bench-arm64.apk`, and `README.md` saying how to run each
+        and what to paste back.
+      **Pass**: Iris's call from the two reports — iris within a reasonable
+      margin of Compose on p50, p99 and CPU time, no crash, no stutter she
+      can see. Fail stops the port.
+
 - [ ] **P1 — session screen parity.** History paging backward (with the
       page-boundary healing `client-core` does not have yet, below),
       `TranscriptSource`-backed cache/server stitching, jump-to-latest,