Re-review returned MERGEABLE with one Low, MySQL-collation-dependent edge in
FlagFileNotFoundByPaths: the C#-side Except diff is ordinal, but `MF.Path IN @LocalPaths`
runs under MySQL's case-insensitive default collation, so a still-reported identified row
differing only in case from an absent legacy row could be matched and flagged missing.
Match on the indexed PathHash instead of collated Path text, and re-state the
NOT EXISTS (JellyfinMusicVideo) guard so the identity pass and the legacy pass are disjoint
by construction rather than by the caller's diff being correct. SQLite was unaffected.
timothy
147166b053