# M3.5.9 — Git-aware memory references: lookup by code location

| Field | Value |
|---|---|
| Phase | M3.5 — Distributed API Layer |
| Size | M — 1–3 days |
| Status | ⬜ Not started |
| Flags | — |
| Spec | inlined below |
| Blocks | — |
| Depends | M3.5.2 (git enrichment in ingest), M3.5.3 (query endpoint) |

## Goal

Enable agents to find and cite memory entries by code location (file:line, commit, author). Unifies memory log with git history. Agents reference: `"Per src/kong/buffer.rs:42 (commit abc123)..."` → lookup via git blame, return L0 evidence + L1 memory.

## Design

**New database columns** (extend `memory_node` from M2.3):
```sql
ALTER TABLE memory_node ADD COLUMN git_context JSONB;
-- {file, line, commit_sha, commit_msg, author, author_date}

-- Index for git-based lookup
CREATE INDEX ON memory_node USING GIN (git_context);
```

**Three lookup modes:**

1. **By git location (file:line):**
```
POST /memory/nodes/by-git
{
  "repo": "github.com/org/poimen",
  "file": "src/kong/buffer.rs",
  "line": 42,
  "project": "poimen"
}
→ 200 {
  "nodes": [
    {
      "sha256": "...",
      "level": "L0",
      "text": "Kong body buffer raised to 16MB...",
      "git_context": {commit_sha, commit_msg, author},
      "created_at": "2026-08-20T..."
    }
  ]
}
```

2. **By commit (evidence from this commit):**
```
POST /memory/nodes/by-commit
{
  "repo": "github.com/org/poimen",
  "commit_sha": "abc123def",
  "project": "poimen"
}
→ nodes from this commit + parent L1/L2 memories
```

3. **By author (what did person X discover):**
```
POST /memory/nodes/by-author
{
  "author": "alice@org.com",
  "project": "poimen"
}
→ L0 nodes created during commits from alice
```

**Query endpoint extension** (M3.5.3):
Add optional `git_repo` param:
```
GET /memory/query?query=Kong&git_repo=github.com/org/poimen&project=poimen
→ results enriched with git_context (file, commit, author)
```

**Response format (all modes):**
```json
{
  "nodes": [
    {
      "sha256": "abc...",
      "level": "L0|L1|L2",
      "brief": "Kong body buffer raised",
      "git_ref": "src/kong/buffer.rs:42",
      "git_commit": {
        "sha": "abc123def",
        "message": "Increase body buffer to 16MB",
        "author": "alice@org.com",
        "date": "2026-08-15T10:30:00Z"
      },
      "parents": [...]
    }
  ],
  "repo": "github.com/org/poimen"
}
```

## Steps

1. `POST /memory/nodes/by-git` handler:
   - Parse `file`, `line`, `project`
   - Query: `SELECT * FROM memory_node WHERE project = $1 AND git_context->>'file' = $2 AND (git_context->>'line')::int = $3`
   - Walk edges to include parent L1/L2 nodes
   - Sort by created_at desc

2. `POST /memory/nodes/by-commit` handler:
   - Parse `commit_sha`, `project`
   - Query: `SELECT * FROM memory_node WHERE project = $1 AND git_context->>'commit_sha' = $2`
   - Include all L0 from this commit + transitive parents (L1/L2)

3. `POST /memory/nodes/by-author` handler:
   - Parse `author`, `project`
   - Query: `SELECT * FROM memory_node WHERE project = $1 AND git_context->>'author' = $2 AND level = 'L0'`
   - Walk edges to L1 parents

4. Extend M3.5.3 query handler:
   - Add optional `git_repo` query param
   - If provided, enrich response with git_context from each result node
   - Include `git_ref` in brief (file:line) for agent citation

5. Deduplication by git:
   - L0 evidence from same (file, line, commit) = same memory entry
   - Idempotency: ingesting same commit twice doesn't duplicate L0 nodes
   - Check: `(file, line, commit_sha)` tuple uniqueness constraint

## Acceptance

- `by-git` lookup returns correct L0 evidence + parent memories
- `by-commit` returns all evidence from that commit
- `by-author` returns all discoveries by that author
- Query results enriched with git_context when repo provided
- Same evidence never duplicated (idempotent by git tuple)
- Agents can cite by code location: "src/kong/buffer.rs:42 (commit abc123)"

## Verify

**Harness:** Integration tests with git history fixture.

**Setup:** Create test repo with commits:
- commit abc123: modify src/kong/buffer.rs:42 (message: "Increase buffer")
- commit def456: modify src/kong/handler.rs:10 (message: "Handle large bodies")
- Create memory nodes with git_context from these commits

**Integration test** — `tests/it_git_references.rs`:
1. `a1_by_git_lookup` — POST /nodes/by-git with file=buffer.rs, line=42 returns L0 from commit abc123.
2. `a2_by_commit_lookup` — POST /nodes/by-commit with abc123 returns both L0 + parent L1/L2.
3. `a3_by_author_lookup` — POST /nodes/by-author with alice@org returns all L0 from alice's commits.
4. `a4_query_enriched_with_git` — GET /query?query=buffer&git_repo=... returns results with git_context populated.
5. `a5_git_ref_in_brief` — result.git_ref = "src/kong/buffer.rs:42" (human-readable).
6. `a6_idempotent_by_git_tuple` — ingest same commit twice, L0 nodes count stays 1 (no duplicates).
7. `a7_edge_walk_preserves_git` — L1 parent of L0 node includes L0's git_context in parents array.
8. `a8_cross_commit_correlation` — two commits affecting same file, both return from by-git lookup (line=0 or range?).
9. `a9_author_query_filters_correctly` — two authors, by-author for alice returns only alice's L0.
10. `a10_missing_git_context_graceful` — old L0 nodes without git_context (from before M3.5.2) still return but git_ref is null.

**Command:** `cargo test -p mem-cli git_references`

**False pass:**
- Git context populated in fixture but never actually extracted from repo.git during ingest (M3.5.2). Test only checks stored data, not enrichment.
- `by-git` returns results but never walks edges to L1. Parent L1 discoveries are invisible.
- Query enrichment tested only with one repo. Multiple repos with overlapping filenames may return wrong results.
- Idempotency tested with same commit but different git_repo URLs (github.com vs gitlab.com). Should be treated differently but test may not catch it.

## Traps

- Git blame is expensive. Caching blames by (file, commit_sha) pair is necessary for repeated queries.
- Line numbers shift with edits. Reference to "line 42" in commit ABC may not match "line 42" in HEAD. Store commit hash, not line number, as primary key.
- JSONB queries in PostgreSQL are slower than indexed columns. Consider denormalizing `git_file`, `git_commit`, `git_author` as separate columns if query volume is high.
- Author name varies (alice@org vs alice.smith@org). Normalize email in ingest or handle fuzzy matching in by-author.
- Cross-repo scenarios: same code in two repos (fork, mirror). git_repo must be part of uniqueness constraint.

---

Background: [DESIGN.md § Distributed API Layer](../DESIGN.md#distributed-api-layer-homelab-frontend)