fix: respond to macOS system playback controls

README.md

@@ -93,6 +93,8 @@ Drag the compact video to move the window; on release, each axis snaps independe
 
 Single-key shortcuts apply only to the playback window and do not intercept text editing, file-picker input, or Command/Control/Option combinations. Held toggle keys do not repeatedly toggle; held `J`/`L` continue seeking and held `,`/`.` continue stepping. `C` captions remains unbound.
 
+macOS media keys and Now Playing controls use native MediaPlayer commands, including while the window is unfocused: play/pause toggles playback, and previous/next seeks backward/forward five seconds instead of switching tracks. System skip controls prefer five-second intervals. Live/non-seekable inputs disable seeking while retaining play/pause. Now Playing reports the current title, duration, elapsed time, and playback state; opening/replacing, closing, failed playback, and quitting release unavailable controls. No Accessibility or Input Monitoring permission is required. macOS chooses which active media app receives the keys.
+
 Initial window setup and returning from the file/YouTube dialogs leave keyboard focus on playback rather than automatically highlighting the titlebar pin. Tab navigation and native focus indicators remain available when choosing controls explicitly.
 
 Frame stepping uses decoded presentation timestamps, not an average-FPS time offset, including variable-frame-rate video and reordered B-frames. Steps start from the displayed frame, stop at the first/last frame, and keep the timeline paused. Consecutive same-direction repeats share one counted queue entry without skipping frames or reordering seeks/direction changes. The last presented image remains visible during decoder preroll and queued steps; the progress thumb follows each authoritative stepped position. Opening/closing media still clears the old image. Audio-only files disable stepping; normal playback resumes with audio synchronized to the selected frame.
@@ -112,6 +114,7 @@ Only implemented actions have controls; there are no placeholder playlist, subti
 - `Sources/Core/output.hpp` and `Sources/macOS/Output.mm`: native output contract, allocation-free/nonblocking Core Audio callback and bounded audio ring, latency-aware presentation clock, retained frame mailbox, and Metal YUV conversion. The view can outlive the player safely.
 - `Sources/App/TerebiApp.swift`: MainActor state polling, file/YouTube panels and Finder/drop handling, cancellable URL resolution, autoplay, video host, AppKit glass and native slider cells, floating controls, visibility, video-fitted sizing, and native window integration. Both accepted open paths enqueue play on the new source's command timeline; the C interface still opens paused for callers that need explicit control.
 - `Sources/App/PlaybackProgress.swift`: local per-video position persistence and canonical file identities, using injectable UserDefaults. The player model checkpoints authoritative positions and defers resumed autoplay until the saved seek is queued against the ready source.
+- `Sources/App/SystemPlaybackControls.swift`: native remote-command registration, main-thread dispatch, Now Playing publication, seekability gating, and target cleanup.
 - `Sources/App/CompactWindow.swift`: same-window compact geometry, saved normal window state, asynchronous fullscreen transitions and failure recovery, all-Spaces/floating behavior, magnetic edge snapping, and its persisted preference.
 - `Sources/App/YouTubeResolver.swift`: YouTube URL and metadata validation, external yt-dlp/runtime discovery, SDR stream selection and headers, bounded nonblocking process output, sanitized extraction errors, and request-local cancellation.
 - `Sources/CLI/PlayerCommand.swift` and `Sources/CLI/TerebiCLI.swift`: command-line validation/help and native application discovery/launching. Launch the app without media first to establish its singleton window, then deliver the selected URL; the app owns Apple events to prevent SwiftUI's default external-document routing from replacing that window.
@@ -140,6 +143,8 @@ Generates short fixtures and exercises the real playback interface and native ou
 
 `make check-runtime` exercises missing/invalid dependency metadata, unavailable ABI libraries, existing but unloadable dylibs, omitted library families, and successful native library loading using isolated app metadata. It is included in `make check`; no installed FFmpeg files are modified.
 
+`make check-media` exercises actual playback through the app model, idempotent play/pause, paused seeking and start-boundary clamping, non-seekable state transitions, and Now Playing cleanup on close/error/shutdown. It is included in `make check` and uses isolated playback history with muted audio. Native MediaPlayer command dispatch was also smoke-checked; physical media-key routing and macOS's choice among competing media apps still need a keyboard check in the running app.
+
 Continuous audio uses resampled sample counts for its output timeline; packet timestamp quantization and rounded resampler delay must not insert silence or drop samples between blocks.
 
 Volume persists across open, seek, and close. Live gain changes ramp over five milliseconds without callback allocation or locking; a stopped output adopts the requested gain before playback starts, so muted startup cannot leak audio.