phase: 167_api_payload_diet

All gates green. Final report:

**Verified (phase 167 final pass — all 6 tasks already in `complete/`)**
- Live re-measure of the headline criterion on the **1,000-doc live-replica corpus** (restored `data/bor_live_kb_replica.dump.sql` into a scratch DB `bor_audit`, alembic 0011→0027, dropped after; the shared dev DB was never touched): `GET /api/docs/tree` default depth=1 = **8,474 identity → 1,128 B with `Content-Encoding: gzip`** (< 40 KB bar; ~2 MB defect fixed), repeat load **304 / 0 bytes**; depth=8 265,147→23,515; node drill 20,844→1,065; `/api/docs` 246,366→45,104; `/api/documents/content` 892,124→60,776 (`LOOK`, accepted-with-why). Reproduces `AUDIT.md` to within 1 byte.
- Transport contracts proven live: `POST /api/chat` **no** `Content-Encoding` + frames arriving live + budget line `… enc=identity duration_ms=7380 stream=1`; HTML still `no-cache` with the `?v=` rewrite (and gzipped); A20 headers on 200 **and** 304; ETag identical across identity/gzip; `depth=0|9|abc`→422; anonymous tree/node→403; unknown folder/source→404 `unknown node`.

**Gates (all 100% green)**
- `uv run pytest` → **3980 passed**; `uv run pytest --cov=app --cov-report=term-missing` → **TOTAL 99%** (`compression.py`, `http_cache.py`, `response_budget.py` 100%; `api/docs.py` 99%, one defensive dedupe line).
- `uv run ruff check .` → All checks passed; `uv run pyright` → 0 errors.
- Phase + regression E2E **in isolation** (`--junitxml`, exit codes): `test_kb_tree_lazy_load` 11, `test_kb_tree` 8, `test_kb_tree_nav` 4, `test_navbar_refresh` 7, `test_document_dates` 6, `test_git_source_dates` 4, `test_sync_summary_visibility` 3, `test_table_ux_polish` 6, `test_sources_midstream_bug` 6, `test_ls_tree_drilldown` 3, `test_smoke` 3 — **0 failures/errors** (the earlier `-q -q` run had simply suppressed pytest's summary line).

**Documentation** — README.md + AGENTS.md reviewed in full (1,436 / 80 lines):
- Fixed (pre-existing, phase-167-exposed): README *Caching & deploys* claimed "One Starlette middleware (`app/core/caching.py`) applies the rule" while the section now describes three transport layers → rewritten to name caching/compression/http_cache, the real outermost→innermost order, and why `bytes=` is uncompressed.
- AGENTS.md rule 5 (UI Structure Check) gained the phase-167 clause: a lazily-drilled level keeps the current level rendered, its in-flight `role="status"` / `role="alert"`+Retry row lives in the same bounded scroll panel, and stat cards read server `totals` (never a walk of a depth-limited tree).
- Cross-checked and consistent: every `BOR_*` in `.env.example` is in the README table, every `Settings` field is documented, all 15 README-cited API routes exist in the app, no stale "one fetch / drill client-side" claim remains anywhere.

**Notable decisions / deviations**
- `compression.py` adds a documented `_RebufferSmallResponses` seam beyond the D1 sketch (the caching layer's `BaseHTTPMiddleware` re-framing otherwise defeats Starlette's `minimum_size` exemption and inflates tiny responses) — integration-pinned, math still Starlette's.
- A node-route **404 = vanished folder → honest reset to top level** (per `00_phase.md` D4/D6), not task-06's "alert + Retry"; 500 shows alert+Retry with the level preserved — both pinned, nothing weakened.
- Retrieval battery not measurable (shared E2E DB holds no corpus), but `git diff --name-only -- app/rag` is empty, so retrieval is unchanged by construction. `AUDIT.md` left byte-identical (it lives under `todo/`, off-limits to this pass); no git index/history commands run.

**Next pending phase:** none — `167_api_payload_diet` is the only entry in `.agents/phases/todo/`; the harness moves it to `complete/` and commits.

tests/e2e/test_sources_midstream_bug.py

@@ -119,9 +119,28 @@ def _run_in_thread(coro: Any) -> Any:
 
 
 def _reset_db(mock_port: int, seed: bool) -> ImportSummary | None:
-    """Truncate the KB (and query log), then optionally re-import fixtures."""
+    """Truncate the KB (and query log), then optionally re-import fixtures.
+
+    The truncate covers EVERY table that shapes the prompt, not just the
+    document rows: this suite's story asserts the EXACT long-answer text,
+    and the mock echoes a stored KB overview into the answer verbatim
+    (`` (kb: <first bullet>)``, phase 31) plus a stored steering note
+    (phase 15). Those rows survive a documents-only truncate — another
+    suite in the shared E2E Postgres ran a real sync and left its
+    overview behind — so the answer would arrive with a suffix this
+    suite never seeded and the byte-exact pin would fail on the OTHER
+    suite's corpus (``tests/e2e/test_kb_tree.py`` is the usual holder).
+    Same list as that suite's ``_truncate_all`` (the house isolation
+    pattern); no assertion changes — the corpus under test is exactly
+    the one this fixture seeds.
+    """
     with SessionLocal() as db:
-        db.execute(text("TRUNCATE chunks, documents, query_log"))
+        db.execute(
+            text(
+                "TRUNCATE chunks, documents, query_log, steering_notes, "
+                "kb_overview, git_sources, folder_summaries"
+            )
+        )
         db.commit()
     if not seed:
         return None