feat(search): retrieval telemetry — log every semantic retrieval

Add retrieval_logs (migration 0068) + services/retrieval_telemetry with a
fire-and-forget record_retrieval(), wired into the MCP search tool
(source=mcp_search) and the REST search route (source=rest_search). Captures
query, effective params, and the per-result score distribution so KB-injection
thresholds can be tuned from data rather than guessed.

Scribe: project 2, milestone 93, task 1032.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Xz4j1H7pjYSjKsEpgcNH5E

tests/test_services_retrieval_telemetry.py

@@ -0,0 +1,112 @@
+"""Tests for services.retrieval_telemetry.
+
+_build_payload is pure (no DB, no loop) and gets unit coverage. The persistence
+path (_insert_retrieval_log + the RetrievalLog model / JSONB roundtrip) is an
+integration test against real Postgres.
+"""
+from types import SimpleNamespace
+
+import pytest
+import pytest_asyncio
+
+from scribe.services.retrieval_telemetry import (
+    _build_payload,
+    record_retrieval,
+)
+
+
+def _note(nid):
+    """Minimal stand-in — _build_payload only reads .id."""
+    return SimpleNamespace(id=nid)
+
+
+# ─── _build_payload (pure) ───────────────────────────────────────────────────
+
+
+def test_build_payload_ranks_and_score_bounds():
+    results = [(0.91, _note(11)), (0.72, _note(22)), (0.55, _note(33))]
+    p = _build_payload(
+        user_id=7, source="mcp_search", query="hello", threshold=0.45,
+        limit=10, project_id=3, is_task=None, results=results, duration_ms=12.345,
+    )
+    assert p["result_count"] == 3
+    assert p["top_score"] == 0.91
+    assert p["min_score"] == 0.55
+    assert [it["rank"] for it in p["result_ids"]] == [0, 1, 2]
+    assert [it["id"] for it in p["result_ids"]] == [11, 22, 33]
+    assert p["duration_ms"] == 12.35  # rounded to 2dp
+    assert p["user_id"] == 7 and p["project_id"] == 3 and p["threshold"] == 0.45
+
+
+def test_build_payload_empty_results():
+    p = _build_payload(
+        user_id=1, source="rest_search", query="x", threshold=0.3,
+        limit=5, project_id=None, is_task=False, results=[], duration_ms=None,
+    )
+    assert p["result_count"] == 0
+    assert p["top_score"] is None and p["min_score"] is None
+    assert p["result_ids"] == []
+    assert p["duration_ms"] is None
+
+
+def test_build_payload_rounds_scores_to_5dp():
+    p = _build_payload(
+        user_id=1, source="mcp_search", query="q", threshold=0.45,
+        limit=1, project_id=None, is_task=None,
+        results=[(0.123456789, _note(1))], duration_ms=0.0,
+    )
+    assert p["result_ids"][0]["score"] == 0.12346
+
+
+def test_record_retrieval_without_event_loop_is_safe():
+    """Called from a sync context (no running loop) it must swallow and return,
+    never raise — telemetry can't be allowed to break a caller."""
+    # No event loop running in this plain sync test.
+    assert record_retrieval(
+        user_id=1, source="mcp_search", query="q", threshold=0.45,
+        limit=10, project_id=None, is_task=None,
+        results=[(0.9, _note(1))],
+    ) is None
+
+
+# ─── persistence (integration) ───────────────────────────────────────────────
+
+
+@pytest_asyncio.fixture
+async def _dispose_engine():
+    from scribe.models import engine
+    yield
+    await engine.dispose()
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_insert_retrieval_log_roundtrip(_dispose_engine):
+    from sqlalchemy import delete, select
+
+    from scribe.models import async_session
+    from scribe.models.retrieval_log import RetrievalLog
+    from scribe.services.retrieval_telemetry import _insert_retrieval_log
+
+    payload = _build_payload(
+        user_id=990001, source="mcp_search", query="pgvector tuning",
+        threshold=0.45, limit=10, project_id=None, is_task=None,
+        results=[(0.88, _note(501)), (0.61, _note(502))], duration_ms=9.9,
+    )
+    await _insert_retrieval_log(payload)
+
+    async with async_session() as s:
+        row = (
+            await s.execute(
+                select(RetrievalLog).where(RetrievalLog.user_id == 990001)
+            )
+        ).scalars().first()
+        assert row is not None
+        assert row.source == "mcp_search"
+        assert row.result_count == 2
+        assert row.top_score == 0.88
+        # JSONB roundtrips as a list of dicts with the expected shape.
+        assert row.result_ids[0] == {"id": 501, "score": 0.88, "rank": 0}
+        assert row.created_at is not None  # server_default now()
+        await s.execute(delete(RetrievalLog).where(RetrievalLog.user_id == 990001))
+        await s.commit()