phase: 112_honesty_gate_weak_hits

**Phase 112 — final verification pass (all 4 tasks already complete in `complete/`):**

- Verified gate fix: `app/api/chat.py::plan_turn` — HIGH iff `best_cosine >= relevance_threshold` OR (`fts_hits > 0` AND `best_cosine >= lexical_support_floor`); `lexical_support_floor` (default 0.35, `BOR_LEXICAL_SUPPORT_FLOOR`, bounds-validated) in `app/config.py` + `.env.example`; A8 revision note (2026-09-14) in `.agents/PLAN.md`.
- Verified prompt contract: `app/rag/prompts.py` diff is docstring-only (dated owner-decision-iii entry); `tests/unit/test_prompt_lock.py` byte-pins PERSONA/TOOLS_SECTION/DEFLECT body (sha256+length).
- Verified README: L11 + L575 deflection copy refreshed; `grep "haven't done anything" README.md` → no hits; disclosed-answer behavior documented.
- Tests: `uv run pytest --cov=app --cov-report=term-missing` → **2378 passed, 99% coverage (>90%)**; includes Mongolia-quadrant unit pins (fts>0 + cosine<floor → LOW).
- E2E in isolation: `uv run pytest tests/e2e/test_honest_deflection.py -v --no-cov` → **4 passed** (out-of-KB question: `deflected=true`, `sources==[]`, 2–3 suggestions); regression `test_chat_rag.py` + `test_retrieval_quality.py` → **7 passed**.
- Lint/types: `uv run ruff check .` → clean; `uv run pyright` → 0 errors.

**Completion criteria:** weak-FTS→LOW unit-pinned ✅ · no false citations + 2–3 alternatives E2E ✅ · prompts byte-identical (test-pinned) + README matches ✅ · suite/coverage/e2e/lint all green ✅ · commit + phase move → left to harness (no `git commit` run, per rules; changes in working tree).

**Deviations:** none. Next pending phase: `113_source_chip_quality`.

app/rag/retriever.py

@@ -21,8 +21,9 @@
   match a document's ``qwen3``/``8``/``27b`` tokens, while every
   unrelated llama.cpp quadlet out-ranks the target on the shared
   ``llama``/``cpp`` tokens). The name-hit rows carry ``fts_hit=True``
-  (they ARE the lexical signal — the A8 honesty gate then answers
-  instead of deflecting) and ``cosine=0.0``; the RRF fusion is
+  (they ARE the lexical signal — the A8 honesty gate answers on them
+  only when the best cosine clears ``BOR_LEXICAL_SUPPORT_FLOOR``,
+  A8 revised 2026-09-14) and ``cosine=0.0``; the RRF fusion is
   unchanged (same lists, same ``1/(k+rank)`` terms).
 * **Fusion** — Reciprocal Rank Fusion (``score = Σ 1/(k + rank)`` over the
   lists a chunk appears in; chunks hit by both lists get both terms). The
@@ -445,7 +446,7 @@ def _name_hit_chunks(db: Session, question: str) -> list[RetrievedChunk]:
                 score=0.0,  # filled in by :func:`fuse`
                 document=doc,
                 cosine=0.0,  # no vector rank — name-only hit
-                fts_hit=True,  # the lexical signal — the A8 gate answers
+                fts_hit=True,  # lexical signal — A8 answers if cosine corroborates
                 is_summary=bool(row.is_summary),
             )
         )