Build the failure context through the title's template builder with an empty MediaInfo, and blank season_episode, absolute and date in season mode. Document {part} and add a docs-to-code parity test.
Delete the dead grouped-download block, the planner, and the music service hooks; Song now flows through the one download loop, gets tagged via tag_file, and answers -w with {disc}x{track} keys.
BREAKING CHANGE: GROUP_AUDIO_DOWNLOADS, get_music_track_options and get_music_collection_label are gone. A music service returns one Audio track per quality and lets the framework choose.
New post_scripts config and repeatable --postscript flag run a command per output, season/album folder, or run, substituting filename-template variables into pre-tokenized argv. The REST API rejects hook commands.
Closes#150