Refactor Player to Programme model

[zeevenn]

Parent

#39 — PRD: AI Radio — Host-driven Channel experience with chat timeline

What to build

Add Radio mode to the Player alongside the existing Classic (queue) mode. The Player supports two playback modes that coexist — only one is active at a time.

Architecture Decision: Preserve Classic Mode

The existing playerStore queue logic (addToQueue, insertNext, removeFromQueue, clearQueue, playQueue, setMode, shuffle) is preserved as-is. Radio mode is additive — it does not replace or remove classic playback. Users can still browse the Library and play tracks manually in queue mode.

What to add (Radio mode)

• A playbackMode: 'radio' | 'classic' discriminator in the player state
• programme: Segment[] and nowPlayingSegmentIndex: number fields (active only in radio mode)
• loadProgramme(programme: Programme) → void — called only by the Programme Manager; automatically switches to radio mode
• onSegmentEnd event (callback or event emitter) so the Programme Manager can react
• Lookahead: pre-load the next Segment while Now Playing is active. Must handle both file URIs (TrackSegment) and remote TTS URLs (InterlSegment)

Mode switching

• loadProgramme() → sets playbackMode: 'radio', stops any classic queue playback
• playTrack() / playQueue() → sets playbackMode: 'classic', stops any radio programme playback
• Only one mode is active at a time

What NOT to change

• All existing queue-mutation actions remain
• PlayMode (single / ordered / shuffle) remains for classic mode
• PlaybackStore (position, volume, rate) is shared between modes
• System controls (lock screen, headphone buttons), audio ducking — unchanged
• Existing tests for classic mode must continue to pass

Acceptance criteria

• playbackMode field exists and correctly reflects which mode is active
• Radio mode: playerStore exposes programme, nowPlayingSegmentIndex, and loadProgramme(programme)
• Radio mode: Player plays a Programme containing both TrackSegments and InterlSegments without errors
• Radio mode: onSegmentEnd fires after each Segment completes
• Radio mode: Lookahead pre-loads the next Segment (Track file URI or remote URL) before Now Playing ends
• Classic mode: all existing queue APIs still work as before
• Mode switching: loadProgramme() stops classic playback; playTrack()/playQueue() stops radio playback
• System controls (lock screen / headphones) work in both modes
• Audio ducking works in both modes
• Tests pass for: mixed-Segment Programme playback, Segment-end events, and existing classic mode behaviour

Blocked by

• Shared types: Segment, Programme, ChatMessage #40 (Shared types: Segment, Programme)