- keep existing /api/image-proxy URLs from being wrapped again
- reuse the shared metadata package instead of duplicating URL logic in web_server.py
- add regression coverage for proxy passthrough and internal URL normalization
- Relocate the shared metadata helper module from core/metadata_common.py into core/metadata/common.py.
- Update the new metadata package, the import pipeline, and the web entrypoint to use the package-scoped helper.
- Keep the shared config, mutagen, file-lock, and tag-writing helpers centralized without touching unrelated files.
- Keep existing metadata_cache and metadata_service at the top level for now
- Move the new branch-local metadata helpers under core/metadata
- Share MusicBrainz release cache state from core.metadata.source and update import sites
