feat: scaffold Brain of Reese — FastAPI RAG chat over Postgres 17 + pgvector

Foundation (phase 01, verified):
- FastAPI app: /api/health, /api/suggestions, /api/chat (placeholder),
  static frontend served locally (no CDN)
- Postgres 17 + pgvector via db/Containerfile + compose.yaml
  (podman compose up -d db), Alembic initial migration (documents,
  chunks with vector(768), query_log)
- LLM client targeting https://aipi.reeseapps.com/v1 (turbo/embed);
  scripts/llm_probe.py verified models + 768-dim embeddings live
- Conditional debugpy: imported only when DEBUGPY=1 (attach on demand,
  :5678); logging config for clean single-line logs
- Frontend shell: mobile-first chat + Sources pages, tokens, a11y baselines
- Tests: 24 unit+integration (99% coverage on app/), ruff + pyright clean,
  Playwright smoke E2E (3 tests) against a deterministic mock LLM
- Planning: .agent/PLAN.md (architecture + LOCKED decisions), AGENTS.md,
  6 user stories, 7 phase files (one story / one phase / one Playwright
  suite each)

.agent/phases/todo/04_story_honest_deflection.md

@@ -0,0 +1,66 @@
+# Phase 04 — Story: Honest Deflection
+
+**Story:** `.agent/user_stories/honest-deflection.md`
+**Context:** `.agent/PLAN.md` §4, §6 (honesty gate), §9
+
+## Goal
+When retrieval finds nothing relevant, Brain says so — plainly, chippily —
+and offers real alternatives. No hallucinated confidence.
+
+## Implementation steps
+1. `app/api/chat.py` — apply the gate: `best_score < settings.relevance_
+   threshold` ⇒ build LOW prompt (`DEFLECT_MODE`, weak-hit titles only),
+   else HIGH prompt. Set `deflected` on the `done` event + `query_log`.
+2. Deflection `suggestions[]`: ask `turbo` (same stream) to include 2–3
+   alternative questions; simplest robust approach — have the LLM emit them
+   inline in the answer AND have the server derive 2–3 chips from the
+   weak-hit document titles (deterministic fallback if the model doesn't
+   produce a parsable list). Ship the deterministic title-derived chips as
+   the v1 behavior; model-generated list is a bonus if trivially parseable.
+3. `frontend/assets/app.js` — on `done.deflected`: add `.is-deflected`
+   class to the bubble, render "Maybe try:" chips below it (same
+   `.suggestion-chip` component; clicking fills the input — full submit
+   behavior lands with Phase 05's chip component; wire what exists).
+4. `README.md` — document `BOR_RELEVANCE_THRESHOLD` tuning + the
+   deflection behavior in Troubleshooting.
+
+## UI Verification
+Against the story: amber bubble (`#fff7e8` bg / `#f59e0b` border) distinct
+from normal answers; "Maybe try:" chips ≥44px, brand-soft/brand-ink;
+contrast pairs verified (ink on accent-bg ≥ 9:1, accent-ink ≥ 8:1);
+chip group has an accessible name; mobile wraps cleanly.
+
+## Testing & Quality
+- Unit: gate boundary with a fake retriever — score exactly 0.30 → HIGH;
+  0.2999 → LOW; LOW prompt contains `DEFLECT_MODE` + titles, no full docs;
+  HIGH unaffected. Suggestions derivation (2–3, non-empty, derived from
+  titles).
+- Integration: mock LLM — off-topic question ("sourdough") ⇒ `done`
+  `deflected: true`, `query_log.deflected=true`, weak `top_score` stored;
+  on-topic question ⇒ `deflected: false`.
+- Coverage: **>90%** on `app/`.
+
+## Playwright Execution Phase
+Run ONLY this story's suite:
+
+```bash
+uv run pytest tests/e2e/test_honest_deflection.py -v --no-cov
+```
+
+Implements the story mapping: off-topic question ⇒ `.is-deflected` bubble
+matching /haven't done anything like that/i + ≥2 "Maybe try:" chips; chip
+click behavior; (unit boundary test lives in pytest, not here).
+
+## Success criteria
+- [ ] off-topic question never gets a confident fake answer
+- [ ] deflected bubble visually distinct + alternative chips render
+- [ ] `query_log.deflected` accurate; threshold env-tunable
+- [ ] unit + integration green, coverage >90%
+- [ ] UI verification passed
+- [ ] story E2E green in isolation
+- [ ] committed
+
+## Commit
+```bash
+git add -A && git commit --no-gpg-sign -m "feat(rag): honest deflection gate with amber UI state and alternative-question chips"
+```