feat(node): share the (path,size,mtime)->hash index cache across every group

2026-08-25T22:40:20Z

An operator routinely shares the same physical folder into more than one group (a music library, a Séries drive) — IndexCache used to be opened once per group (data_dir/{group_id}/index_cache.db), so the second group to reference an already-fully-hashed multi-terabyte folder paid the same full content read the first one did. IndexCache itself carried no group_id in its schema; only daemon.py's wiring did. Now one instance, opened once at startup (data_dir/index_cache.db), shared by every group's DirectoryIndexer. Confirmed against a real deployment (2026-08-25/26): a group sharing an already-indexed folder with an existing group indexes it instantly, with zero rehashing. Also fixes a related cross-group correctness gap found during this work: media_cache.db (thumbnails, TMDB/MusicBrainz metadata — already node-wide, untouched by this change) was pruned for a file the moment it left *one* group's index, even if another group's index still held the same content hash — forcing a redundant re-fetch/re-probe/re-thumbnail for a group that never actually lost anything. Prune now runs only once no group's index references the file_id any more. Adds a node admin UI action ("Maintenance" card, prune-index-cache) to drop cache rows that no longer belong to any group's roots — skips anything under a root that is merely temporarily unavailable (indexer.py's "a root that goes away freezes, never empties" rule extends to this cache too, or a reconnected drive would pay a full rehash for no reason). Co-Authored-By: Claude Sonnet 5 Claude-Session: https://claude.ai/code/session_013XSohfUQQiaE77qyFLgSv3

meshbay.git/packages/meshbay-node/tests/test_ops_index_cache.py, branch 0.13

feat(node): share the (path,size,mtime)->hash index cache across every group