Documents every currently-registered OpenSubsonic extension
(apiKeyAuthentication, formPost, getPodcastEpisode, songLyrics,
indexBasedQueue, playbackReport, topSongsByArtistId, transcodeOffset,
transcoding, sonicSimilarity), what backs each one, and what it's
tested against — cross-referencing the extensions-registry regression
guard that fails the build if an advertised extension's handler ever
goes missing. Also updates the getArtistInfo/getAlbumInfo/
getSimilarSongs rows and error-code list for Phase 3 changes.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014r98AtcBbevpscWLsfwVvv
owenandClaude Sonnet 5