`core/media_server/` package with the Protocol contract that
every media server client (Plex, Jellyfin, Navidrome, SoulSync
standalone) satisfies, plus the registry that holds them.
Required methods conservatively limited to the four every server
truly implements today: is_connected, ensure_connection,
get_all_artists, get_all_album_ids. Other generic methods
(search_tracks, trigger_library_scan, get_recently_added_albums,
etc.) are listed as OPTIONAL — present on most servers but not
all (SoulSync has no library-scan API since it walks the filesystem
directly; Jellyfin uses a different search shape). Phase B's
engine adapters route around the gaps with per-server fallback
instead of forcing every client to declare a no-op stub.
Same registry shape as the download plugin registry — single
source of truth for which servers exist + name resolution. Adding
a 5th server (Subsonic, Emby, etc.) becomes one register call
plus the new client class.
5 conformance tests pin every server class implements every
required method. Plan doc at docs/media-server-engine-refactor-plan.md.
Pure additive — no consumer routes through the contract or
registry yet. Suite still green (1921 passed).
Broque Thomas