Add a comment at the deletion-tracking scroll noting that a user who
gained access to a shared file via the tenant-wide dedup path (without
indexing it) is absent from the user_id-filtered indexed_file_ids, so the
grace-period sweep never enqueues a delete for them — their stale
acl_principals entry is reclaimed lazily by verify-on-read eviction.
Addresses review nit #3.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>