A successful fetch returning zero items made existing.Except([]) flag the ENTIRE
library FileNotFound in one scan — feeding EmptyTrashHandler's permanent delete
and emptying every affected collection (dead channels). Add a shared
MediaServerReconciliationGuard that skips (and logs a Warning) the sweep when
incoming==0 while items exist, wired into the three library-level sweeps
(Television shows / Movie / OtherVideo).
An empty incoming set is indistinguishable at scan time from a mid-restore /
emptied-upstream error (both report a zero total), so this deliberately overrides
#476's degenerate "last item removed => empty incoming => flag" case. #476's
cascade still fires for partial deletions (survivors present); its characterization
test moves from an empty incoming to a survivor+removed partial-deletion case.
Tests: policy table (MediaServerReconciliationGuardTests) + per-scanner integration
proving the wiring (empty incoming + non-empty existing flags/reindexes nothing).
Proven non-vacuous by neutralizing the guard. Nested TV season/episode sweeps left
unguarded (bounded blast radius); ratio-threshold + projection-failure detection
deferred to a follow-up. docs/decisions.md updated.
Fixes#477
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
