Stopping a remote session left Android stuck on the remote volume slider
with no way back to the device speaker.
Two causes:
1. `player_stop`'s remote branch sent "Stop" to the session and returned
without touching the playback mode, so the manager stayed in Remote.
It now drops to Idle, mirroring what the local branch already does.
2. Volume routing was torn down at a single call site
(`transfer_to_local_inner`), so every *other* exit from remote mode
leaked the Android VolumeProviderCompat. Routing is now derived from
the transition inside `set_mode`: entering remote attaches control,
any exit from remote hands it back to the local media stream. This
also covers the frontend `disconnect()` path (Remote -> Idle) and the
local-playback-start paths (Remote -> Local).
Adds a `RemoteVolumeControl` trait so the routing rule is unit-testable
off-device — the real implementation is Android JNI. Tests cover
remote->idle, remote->local, remote->remote (re-arms, never releases),
and that local/idle transitions leave routing untouched.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
dtourolleandClaude Opus 5
2ca2174cea