An episode handed off to the audio-only path for background playback is a
MediaType::Audio item, so autoplay's video-only checks stopped
recognising it as an episode: playback simply ended at the episode
boundary instead of continuing to the next one.
- Carry episode identity (item_type, series_id) through the
background-audio handoff so the backend queue item still knows it's an
episode; is_episode_item now trusts item_type over the media_type
heuristic, and the sleep timer's episode counter follows.
- The frontend normally performs the advance by navigating to
/player/<id>, which is unavailable while the WebView is suspended.
advance_to_next_episode_audio_only drives it entirely in the backend:
fetch the next episode, build its audio-only stream URL, and load it
into the native audio player, preserving episode identity so the
following boundary advances too.
- Android's autoplay dispatch routes background-audio episodes to that
backend advance and keeps the countdown path for the foreground.
- get_audio_only_stream_url_for_video joins the MediaRepository trait
(online delegates to the existing builder, offline errors) so the
controller can reach it without a frontend round-trip.
TRACES: UR-040, UR-023 | DR-052 | JA-032