docs: README + device testing checklist (Phase 9)

docs/DEVICE_TESTING.md

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+# Device testing checklist
+
+Simulator verification covered connect/disconnect, transcripts (text mode), media
+reconciliation/UI, tasks panel, and the hardening pass. The items below need a **real
+iPhone on the LAN** (`https://192.168.86.2:9178`) because mic input, WebRTC capture,
+and audio session behavior don't work in this simulator environment (CoreAudio `-4010`,
+0 input channels).
+
+Setup: build with Xcode for a physical device (or `xcodebuild ... -destination`), install,
+ensure the server cert pin is current (see README — re-export after any server restart).
+
+## 1. Mic input with real speech
+
+- [ ] Start → agent joins → mic enables **without** `-4010`.
+- [ ] Speak: orb/status transitions to **listening**; mic meter moves with voice level.
+- [ ] Stop speaking, wait >2 s while agent is silent → **thinking** chip appears.
+- [ ] Agent replies: state goes to **speaking** (remote audio drives it), TTS audible.
+- [ ] User transcript finals arrive in the list with correct role/timestamps.
+
+## 2. Barge-in
+
+- [ ] While the agent is speaking, start talking → conversation continues without a
+    "barge-in" glitch; state returns to listening/thinking as expected.
+- [ ] Text mode: barge-in hint line visible while in text mode.
+
+## 3. Wake lock (screen off)
+
+- [ ] During an active conversation, press the side button (screen off).
+- [ ] Screen stays on / auto-lock is suppressed for the duration of the session
+    (`isIdleTimerDisabled`); after hang-up, auto-lock returns.
+
+## 4. Audible media playback
+
+- [ ] Requires a track in an iOS-decodable format (m4a/aac/mp3) — current library tracks
+    are webm and will fail with `-11828` until the server serves a supported format.
+- [ ] Play a library track: audio is audible, now-playing card shows art/title/status.
+- [ ] Pause / ±10 s / stop / seek all work; agent mics off while playing
+    (`media_state` published), mics back on when stopped.
+- [ ] End conversation while music was playing before → playback resumes.
+
+## 5. Audio interruption (phone call / Siri)
+
+- [ ] Mid-conversation, trigger an interruption (incoming call or "Hey Siri").
+- [ ] Mic is muted on interruption begin; conversation/media pause cleanly.
+- [ ] On end (with `shouldResume`), mic and media resume automatically.
+- [ ] Media panel: AVPlayer pauses on interruption and resumes after.
+
+## 6. Mic permission denied fallback
+
+- [ ] Deny microphone permission in iOS Settings for the app, relaunch.
+- [ ] Start → session reaches **ready** despite mic failure (non-fatal); orange error
+    banner shows the mic error; text mode remains fully usable.
+
+## 7. General device sanity
+
+- [ ] Connect / hang-up / reconnect matrix (3×) — no crashes, state resets cleanly.
+- [ ] Change server URL in Settings while idle → session recreates without crash.
+- [ ] Reconnect banner appears on network loss mid-call; recovers on return.
+- [ ] Voice/model picker changes take effect live on the agent and survive relaunch.