fix(media-watcher): write playback as discrete per-player segments

[0xbrayo]

Part of #333.

MediaWatcher sent playback as zero-duration heartbeats (pulsetime 60s) on every change and every 15s poll. The server only merges a heartbeat into the newest event in the bucket. With two media sessions playing at once (for example music plus a video), their heartbeats alternated, so neither ever merged, and every poll inserted two new zero-duration events instead of extending two events.

Change

• New MediaPlaybackSegments tracks one open segment per media session (keyed by session token, so an app's two sessions stay separate) with a known start. It writes the segment once, with its real duration via insertEvent, when:
  • the track or playback state changes,
  • the session is destroyed, leaves the active list, or the listener disconnects,
  • the player pauses or stops without metadata, or reports an unknown state or empty metadata,
  • the segment reaches 5 minutes, after which a new segment starts.
• The 5-minute chunking bounds how much is lost if the process is killed mid-episode, and how stale the bucket gets during long playback. Contiguous chunks from the same player still merge on the server when nothing else was written in between.
• Pause, stop and buffering transitions are still recorded as zero-duration events, once per transition, as before.
• All segment work, including the final writes on disconnect and destroy, runs on the watcher's handler thread, never the service's main thread.
• Event data is unchanged: app, package, title, artist, album, state.

Behaviour change

Playing time now shows up when the segment closes, at most ~5 minutes plus one poll later, rather than being extended live by heartbeats.

Testing

• New MediaPlaybackSegmentsTest covers:
  • two players polled together write one event each instead of an event per poll,
  • a track change ends the previous track,
  • long playback is written in bounded chunks,
  • a repeated pause is recorded once.
• ./gradlew :mobile:testStandardDebugUnitTest passes.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no new actionable issue was found.

Summary

The PR replaces media heartbeats with completed playback segments, tracked separately for each media session.

• Playing segments close on track changes, playback changes, session removal, or the five-minute limit.
• The latest changes put registration and teardown on the same worker thread.
• The earlier findings were rechecked. No new actionable issue was found in the changes since the last review.

Diagram

sequenceDiagram
    participant Android
    participant Worker as MediaWatcher worker
    participant Segments as Per-session segments
    participant Store as Media bucket
    Android->>Worker: Connect and scan sessions
    Worker->>Segments: Observe playback
    Android->>Worker: Track change, pause, or session removal
    Worker->>Segments: Close affected segment
    Segments->>Store: Write start, duration, and media data
    Android->>Worker: Queue teardown at disconnect time
    Worker->>Worker: Finish running scan, then unregister callbacks
    Worker->>Segments: End remaining segments at disconnect time
    Segments->>Store: Write final playback

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_{Reviews (3) · Last reviewed commit: "fix(media-watcher): serialize teardown w..." · Reviewed by Greptile}

[0xbrayo]

🤖 Claude, on behalf of @0xbrayo

@greptile review

[0xbrayo]

🤖 Claude, on behalf of @0xbrayo

@greptile review