User reported nothing happening on a chaotic staging root despite
6 candidates being detected. Logs showed "Processing folder" for 3
of 6 — the other 3 were silently skipped.
Root cause:
The previous commit (`a9a6168`) introduced loose-file grouping —
multiple `FolderCandidate` objects can now share a `path` (each
album group at the staging root has the same parent directory but
its own audio_files + folder_hash). But two pieces of dedup
machinery still keyed on `path`:
- `_processing_hashes` (was `_processing_paths`) — runtime set of
in-flight candidates. Path-keyed → first sibling marks the path,
second + third siblings hit "already in flight" and skip.
- `_folder_snapshots` — mtime cache for stability check. Path-keyed
→ siblings overwrite each other's mtimes, stability check returns
unreliable results for whichever sibling lost the write race.
Both kept track of an attribute that was previously unique-per-path
(one candidate per directory) but my refactor broke that
invariant without updating the dedup keys. Net effect: only the
first candidate per directory ever got processed in a chaotic-root
scenario.
Fix:
- Renamed `_processing_paths` → `_processing_hashes` set, keyed on
`candidate.folder_hash`. Hash is unique per candidate by
construction (different audio_files lists hash differently).
- `_folder_snapshots` retyped + rekeyed to `folder_hash`. Siblings
no longer overwrite each other's mtime tracking.
- Both touched in lockstep — comments document why path-keyed
dedup breaks for sibling candidates.
Test added (`test_sibling_candidates_have_unique_folder_hashes`):
verifies 3-album loose root produces 3 candidates with distinct
folder_hashes. If a future change breaks the invariant, the test
fails before the silent-skip regression ships.
Verification:
- 178 imports tests pass (8 new this commit + 170 pre-existing
this branch)
- Ruff clean
- Still scoped to import flow
a478747a89