Standalone _run_soulsync_deep_scan did a path-only diff (untracked = transfer files
not in the soulsync DB) and shutil.move'd EVERY untracked file to Staging — no guard.
When the DB is empty/out of sync with disk (volume swap, DB reset, external Picard
tag edits) but Transfer holds the real library, that flags the whole library as
untracked and relocates all of it; Phase 5 then deletes the rows, and with Staging
cleanup on the files are gone for good. Reporter lost ~1,500 tracks into Staging.
The stale_guard the orphan detector + media-server deep scan already use (#828, #908)
was never wired into this path. Fix:
- core/library/standalone_scan.py (pure, tested): plan_standalone_deep_scan() diffs
untracked (separator-normalized) and decides whether the move is safe. Blocks when
the untracked share is implausibly large (>20 files AND >50% of Transfer — the
desync signature, via is_implausible_orphan_flood) or when the user marked Transfer
permanent. A normal batch of new arrivals still moves.
- web_server: consult the planner before Phase 4; on block, move NOTHING, leave files
in place, and surface a loud warning + activity item. Guard Phase 5 deletes too
(skip on desync-block or implausible stale share).
- 'Transfer is my permanent library — never move files out' toggle
(import.transfer_is_permanent) in Settings.
- tests/library/test_standalone_scan.py: seam coverage + the #904 regression
(empty DB + 1,500 files -> blocked, nothing moved).
No behavior change for in-sync libraries; the guard only trips on the desync pattern.
