Read-only passthrough FUSE filesystem presenting a virtually reorganized,
re-tagged view of a music library backed by SQLite, without modifying or
duplicating the original audio bytes.

Delivered:
- FLAC + MP3 metadata synthesis spliced in front of byte-identical backing audio
- Embedded art synthesized and streamed (never materialized), deduped in-store
- beets-style path templates with fallbacks + collision disambiguation
- synthesis and structure-only (passthrough) mount modes
- automatic refresh on external DB edits via PRAGMA data_version polling
- scan + scan --revalidate (skip-unchanged, prune-missing, GC orphan art)
- CLI: musefs scan / musefs mount

Post-MVP work is tracked in docs/ROADMAP.md.