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+# RCA: Identity UUID Missing + File Identities First/Last Appearance NULL
+
+**Date**: 2026-05-15
+**Author**: M5
+**Status**: Resolved
+
+---
+
+## Summary
+
+Two related defects in the identity listing endpoints prevented external systems from using `identity_uuid` for further API calls, and returned null time ranges for face identities.
+
+| Issue | Endpoint | Symptom | Severity |
+|-------|----------|---------|:--------:|
+| #2 | `GET /api/v1/identities`<br>`GET /api/v1/file/:file_uuid/identities` | Response missing `identity_uuid` | High |
+| #3 | `GET /api/v1/file/:file_uuid/identities` | `first_appearance` / `last_appearance` always `null` | Medium |
+
+---
+
+## Issue #2 — identity_uuid Missing
+
+### Root Cause
+
+Two list endpoints only returned `identity_id` (integer primary key) without `identity_uuid` (public UUID):
+
+```json
+// GET /api/v1/identities — before fix
+[{"id": 18276, "name": "PERSON_aeed7134_367", "metadata": {}}]
+```
+
+```json
+// GET /api/v1/file/:uuid/identities — before fix
+{"identity_id": 18276, "name": "PERSON_aeed7134_367", ...}
+```
+
+The `identities` table has both columns:
+- `id` (SERIAL INTEGER) — internal FK, used in `face_detections.identity_id`
+- `uuid` (UUID, `gen_random_uuid()`) — stable external identifier
+
+All identity detail/chunks/files/bind routes require `identity_uuid` in the URL path (`/api/v1/identity/:identity_uuid/...`). Without it in the list response, clients had no way to navigate from a list entry to its detail.
+
+### Code Location
+
+| File | Line | Issue |
+|------|------|-------|
+| `src/api/identities.rs:177` | SQL query | `SELECT id, name, metadata FROM identities` — missing `uuid` |
+| `src/api/identities.rs:197-200` | Response mapping | `IdentityResponse { id, name, metadata }` — no `identity_uuid` |
+| `src/api/identity_api.rs:206-217` | Response mapping | `FileIdentityItem { identity_id, name, ... }` — no `identity_uuid` |
+| `src/core/db/postgres_db.rs:2405-2418` | DB query | `get_file_identities` SELECT missing `i.uuid` |
+
+### Timeline
+
+| When | What |
+|------|------|
+| V4.0 | `identity_uuid` existed in DB schema and detail endpoints, but list endpoints never included it |
+| 2026-05-14 | M4 reported inability to navigate from identity list to detail/files |
+| 2026-05-15 | Fixed in `37799ff` |
+
+### Fix
+
+1. **`GET /api/v1/identities`** (`identities.rs`): Query changed to `SELECT id, uuid, name, metadata`; response struct `IdentityResponse` added `identity_uuid: String`
+2. **`GET /api/v1/file/:uuid/identities`** (`identity_api.rs` + `postgres_db.rs`): `FileIdentityRecord` added `identity_uuid: Option<uuid::Uuid>`; SQL added `i.uuid as identity_uuid`; GROUP BY updated to include `i.uuid`
+
+### Lesson
+
+**All list endpoints should expose the stable UUID of the resource, not just the internal integer ID.** The external API surface is UUID-based (`:identity_uuid` in routes), so any endpoint that returns identity references must include the UUID.
+
+---
+
+## Issue #3 — first_appearance / last_appearance Always NULL
+
+### Root Cause
+
+The SQL query in `get_file_identities()` hardcoded `NULL::float8` for both fields instead of computing actual frame ranges:
+
+```sql
+-- Before fix
+SELECT 0 as id, fd.file_uuid, fd.identity_id::int4, i.name, i.metadata,
+       COUNT(*)::int4 as face_count,
+       0::int4 as speaker_count,
+       NULL::float8 as first_appearance,   -- ← hardcoded NULL
+       NULL::float8 as last_appearance,    -- ← hardcoded NULL
+       AVG(fd.confidence)::float8 as confidence
+FROM face_detections fd
+JOIN identities i ON fd.identity_id = i.id
+```
+
+### Code Location
+
+| File | Line | Issue |
+|------|------|-------|
+| `src/core/db/postgres_db.rs:2409-2410` | SQL query | `NULL::float8 as first_appearance, NULL::float8 as last_appearance` |
+
+The data was available (`face_detections.frame_number`) but never queried. This appears to have been a placeholder left during initial development that was never implemented.
+
+### Timeline
+
+| When | What |
+|------|------|
+| V1.0 (initial) | Query written with `NULL::float8` — never implemented |
+| 2026-05-14 | M4 report mentioned identity data quality issues |
+| 2026-05-15 | Fixed in `fdcec82` |
+
+### Fix
+
+Replaced with actual aggregate queries:
+
+```sql
+-- After fix
+MIN(fd.frame_number) as start_frame,
+MAX(fd.frame_number) as end_frame,
+```
+
+Time values are computed in Rust from frame + fps:
+```rust
+start_time: r.start_frame.map(|sf| sf as f64 / r.fps),
+end_time: r.end_frame.map(|ef| ef as f64 / r.fps),
+```
+
+Also renamed fields to match naming convention:
+- `first_appearance` → `start_frame`
+- `last_appearance` → `end_frame`
+- Added `start_time`, `end_time`, `fps`
+
+### Lesson
+
+**Do not commit placeholder SQL with hardcoded NULL values.** If a field is not yet implemented, either omit it from the response or mark it explicitly as `"not_implemented"` rather than returning `null` which suggests the data exists but is missing.
+
+---
+
+## Related Commits
+
+| Commit | Fix |
+|--------|-----|
+| `fdcec82` | Issue #3: Start/end frame + time + fps |
+| `37799ff` | Issue #2: identity_uuid in list responses |
+
+## Affected Files
+
+| File | Changes |
+|------|---------|
+| `src/api/identities.rs` | SQL query + struct + mapping to include `uuid` |
+| `src/api/identity_api.rs` | `FileIdentityItem` + response struct + mapping |
+| `src/core/db/postgres_db.rs` | `get_file_identities` query + `FileIdentityRecord` |