Three unrelated fixes rolled into one so testing on the tablet stayed
coherent. All were driven by what the user was observing during live
audio tests, not by pre-planned refactors.
1. **Audio playback actually audible.** ColorOS's AudioFlinger
silently muted our AudioTrack ~600 ms after play() every time
(dumpsys audio showed `event:muted updated source:clientVolume`
and playbackHeadPosition stuck at 0), regardless of USAGE_MEDIA /
USAGE_ASSISTANT / USAGE_VOICE_COMMUNICATION, regardless of audio
focus grant, regardless of FGS type including mediaPlayback. A
MediaPlayer path using the SAME usage attributes works because it
routes through a different AudioFlinger thread that isn't under
the same background-hardening policy. `USE_MEDIAPLAYER_FALLBACK`
in Qwen3TtsEngine.kt flips playback to a WAV-per-segment pipeline.
Two MediaPlayer instances are chained via `setNextMediaPlayer()`
so segments transition without re-arming the DAC (that re-arm was
audible as "beg beg" pops between sentences). Synth of seg N+1
runs in parallel with playback of seg N via a capacity-2 Channel,
hiding synthesis latency behind playback for all but the first seg.
2. **Mic no longer loops TTS back into STT.** The continuous-
listening VAD in KazeiaService already had a guard to drop frames
while `pipelineState is Speaking`, but that state was never set by
any caller — so the mic kept recording during playback and fed our
own speaker output back to Whisper, creating the infinite
"Kazeia talks to Kazeia" loop the user observed. Both the
stream_llm intent path and the main `processLlmResponse` TTS path
now wrap the TTS call with `Speaking → Idle/Listening`.
3. **Free 1.6 GB of RAM at service start.** The OnePlus Pad 3 with
ColorOS keeps ~7 GB of Google + OPLUS background services
resident at idle. With Qwen3-4B (3.2 GB) + Qwen3-TTS (1 GB) +
Whisper (0.5 GB) on top, most of our model weights were going to
ZRAM swap — "the NPU is stuck" reports were actually page faults
paging 3 GB of LLM weights back in before each inference. New
`MemoryOptimizer` kills 30-ish non-essential background packages
(Google optional: YouTube, Wallet, Chromecast, Messaging, AICore,
Quicksearchbox; OPLUS optional: smartsidebar, cosa, pantanal,
nhs, midas, …) via `ActivityManager.killBackgroundProcesses`.
Measured reclaim on first run: **avail RAM 8468 MB → 10112 MB,
+1644 MB**. Uses KILL_BACKGROUND_PROCESSES (normal perm, no user
prompt); system-critical packages and the launcher/systemui are
explicitly excluded from the target list.
Collateral changes:
- Added FOREGROUND_SERVICE_MEDIA_PLAYBACK permission + fgsType flag
(didn't fix the mute on its own, but it's correct per Android 14
policy and leaving it without would be a latent compliance risk).
- Kept `USE_STREAMING_DECODE` + CP↔BigVGAN overlap code intact
behind the MediaPlayer-fallback branch so reverting to the
AudioTrack streaming path is a single-const flip if ColorOS ever
lifts the hardening (or we move to a device without it).
- New AudioTrack path has a keep-alive silence watchdog and a
playback-head drain wait on stop. Both were attempts to fix the
mute that didn't pan out on their own; leaving them in so the
streaming path stays usable on non-hardened devices.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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