Branch B of the multi-library data-model rollout. tagged_photo and
photo_insights now follow the bytes (content_hash), not the path,
matching the policy pinned in CLAUDE.md "Multi-library data model".
Branch A's availability probe and EXIF scoping land first; this
branch builds on top.
Migration (2026-05-01-000000_hash_keyed_derived_data)
Adds nullable content_hash columns to tagged_photo and photo_insights,
with partial indexes on the non-null subset to keep the index small
during the transitional window. The migration backfills from
image_exif:
* tagged_photo joins on rel_path alone (no library_id available);
* photo_insights joins on (library_id, rel_path), unambiguous.
Rows whose image_exif hash isn't known yet stay null and the runtime
reconciliation pass populates them as the hash backlog drains.
Insert-time population
TagDao::tag_file looks up image_exif.content_hash by rel_path before
inserting; the hash is written into the new column.
InsightDao::store_insight does the same scoped to (library_id,
rel_path). Caller-supplied hash on InsertPhotoInsight wins; otherwise
the DAO does the lookup. Both paths fall back to None if the hash
isn't known yet — reconciliation backfills.
Reconciliation (database/reconcile.rs)
Three idempotent passes the watcher runs once per tick after the
per-library backfill loop:
1. tagged_photo NULL hashes → populate from image_exif by rel_path.
2. photo_insights NULL hashes → populate by (library_id, rel_path).
3. photo_insights scalar merge — when multiple is_current rows
share a content_hash, keep the earliest generated_at as
current; demote the rest. Demoted rows keep their data so
/insights/history is unaffected; only the "current" pointer
narrows to one per hash.
No filesystem dependency, so reconcile doesn't need the availability
gate; runs every tick. Logs once when something changed, debug
otherwise.
Tags are set-valued under the policy (union on read, already
DISTINCT in queries), so there is no analogous tag-collapse pass —
duplicate (tag_id, content_hash) rows across libraries are
harmless.
Read paths are unchanged in this branch — lookup_tags_batch's
existing rel_path-via-hash-sibling expansion still produces the
correct merge. A follow-up can simplify reads to use the new column
directly for performance.
Tests: 217 pass (212 pre-existing + 5 new in reconcile covering
NULL-fill, hash-not-yet-known no-op, library scoping on insights,
earliest-wins collapse, idempotency).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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