phase: 94_ls_tree_drilldown

All green. Verification complete.

**Phase 94 — `ls` drill-down tree: final verification pass (all 5 tasks were already complete; verified, nothing to fix)**

- Verified `ls` 3-level tree (`app/rag/agent.py`): `ls()` sources + summaries, `ls(source)`/`ls(source/folder)` drill-down, 50-line file cap + grep-pointer note, NOT-A-FOLDER teaching refusal
- Verified `folder_summaries` (migration 0017, model, `app/rag/folder_summaries.py` generator: `FOLDER_SUMMARY_MODE` marker, fail-soft per folder, ≥2-doc scope + prune) wired change-gated in both sync paths
- Verified 10-turn fixture battery verdict recorded in `TOOL_CALLING_TESTING.md` §9 (2026-09-11): turbo PASS 19/19 contract, 98.7 s (−12.5…−13.2 % vs baseline); lite PASS 18/18, 43.6 s (+7.7 %) — accuracy at/above baseline, gate met
- `uv run pytest --cov=app --cov-report=term-missing` → 1939 passed, 0 failed; TOTAL coverage **99 %** (folder_summaries.py 100 %)
- `uv run ruff check .` → clean; `uv run pyright` → 0 errors, 0 warnings
- E2E in isolation: `test_ls_tree_drilldown.py` 3 passed; `test_agent_document_tools` 4, `test_agent_unlimited_tools` 4, `test_harness_aligned_tools` 3, `test_search_tool` 3, `test_grep_regex_teaching` 2, `test_response_to_docs` 4 — all passed (read/grep contracts untouched)
- Dedicated folder-summary tests (fail-soft, prune, both sync paths, migration): 46 passed
- Completion criteria: all 6 met; working tree holds only phase-94 changes (commit left to harness per protocol)

**Next pending phase:** `95_read_truncation_cap`

tests/integration/test_chat_api.py

@@ -943,7 +943,10 @@ def test_tool_execution_db_failure_yields_error_event(
     def boom(*_a: Any, **_k: Any) -> Any:
         raise RuntimeError("db exploded mid tool call")
 
-    monkeypatch.setattr(agent, "list_catalog", boom)
+    # Phase 94: the no-arg ``ls`` executes through ``ls_top`` — the
+    # failure hook moves with the rewrite (same contract: the tool
+    # frame goes out first, the structured error ends the turn).
+    monkeypatch.setattr(agent, "ls_top", boom)
     fastapi_app.dependency_overrides[chat_api.get_llm] = lambda: scripted
     try:
         _, _, frames = _stream_chat(client, QUESTION)