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`

app/config.py

@@ -135,6 +135,14 @@ class Settings(BaseSettings):
     #: ``app.rag.overview``). Overflow is cut at the cap and the shared
     #: ``[…truncated…]`` marker is appended (summarizer convention).
     overview_input_max_chars: int = 40_000
+    #: Cap on the folder document list (path/title/first summary line per
+    #: row) sent to the ``lite`` folder-summary model in ONE call
+    #: (phase 94, ``app.rag.folder_summaries``). Overflow is cut at the
+    #: cap and the shared ``[…truncated…]`` marker is appended
+    #: (summarizer convention). Smaller than the KB-overview cap on
+    #: purpose: a folder sees its own subtree only — there can be
+    #: hundreds of folders, each summarized separately at sync time.
+    folder_summary_input_max_chars: int = 8_000
     #: Hard cap on the agent tool rounds per grounded turn (phase 45,
     #: revising phase 37's per-tool budgets — owner permission
     #: 2026-08-27, TODO L8: "allow the LLM to make as many tool calls