Fast-follow of #54. After the #52 idle/dismiss teardown, pressing play
on a headset / watch / lock screen did nothing (handler.play() was just
_player.play() with nothing loaded; the handler is Riverpod-agnostic).
- audio_handler: _resumeHook + setResumeHook(); play() is now async —
when mediaItem == null and a hook is set it awaits the hook (which
restores + plays) and returns, else _player.play()
- resume_controller: extract shared _loadAndRestore() (bool); _restore()
keeps the paused launch path; new resumeFromMediaButton() restores
then starts playback; start() registers it via setResumeHook
Recursion-safe (post-restore mediaItem != null so the re-play hits
_player.play()); no-op when nothing to resume / auth missing / a
session is already active.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen
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