diff --git a/docs/DECISIONS.md b/docs/DECISIONS.md
index d02118e..656939e 100644
--- a/docs/DECISIONS.md
+++ b/docs/DECISIONS.md
@@ -7,6 +7,21 @@ marked **DEFERRED** are ones the agent chose not to decide alone.
 
 ## 2026-09-05
 
+- **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
diff --git a/docs/RUST.md b/docs/RUST.md
index 05e07f8..5c40427 100644
--- a/docs/RUST.md
+++ b/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,