New flat per-file holder set replaces the directional upstream/downstream
trees. Keyed by 32-byte content-addressed file_id (works for both PostId
and blob CID). LRU-capped at 5 holders per file on touch.
- HolderDirection enum (Sent/Received/Both) — tracked for potential
reuse, not load-bearing for propagation
- touch_file_holder / get_file_holders / delete_file_holders
- seed_file_holders_from_legacy: one-time idempotent seed from
post_upstream, post_downstream, blob_upstream, blob_downstream so
users upgrading from 0.6.0 don't start with empty holder sets
Table and methods land here; call-site refactor and legacy-table drop
follow in subsequent commits within this phase.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
1658762a68