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/06_story_loading_feedback.md

@@ -0,0 +1,64 @@
+# Phase 06 — Story: Loading Feedback & Progress
+
+**Story:** `.agent/user_stories/loading-feedback.md`
+**Context:** `.agent/PLAN.md` §7.4 ("never stale" contract), §9
+
+## Goal
+An unambiguous state machine — `idle → thinking → streaming → done |
+error → idle` — so the user always knows what's happening, and a stale
+Send button is impossible.
+
+## Implementation steps
+1. `app.js` — formalize the state machine (single `setUiState(state)`
+   function driving: typing indicator, send button disabled/spinner/label,
+   `#send-status` live text). Replace ad-hoc busy handling from Phase 03.
+2. Pre-token: typing indicator (`role="status"`,
+   `aria-label="Brain of Reese is thinking"`); after 10s pre-token, update
+   the label with elapsed seconds (setInterval, cleared on state change).
+3. Streaming: first `delta` removes the typing indicator and starts
+   appending to the answer bubble; button stays busy.
+4. Error paths: `{"type":"error"}` SSE event, non-2xx response, or
+   **120s client-side timeout** (clear on first delta) → red banner
+   `role="alert"` ("Try again — if this persists, check the LLM is
+   reachable") + state → idle.
+5. `prefers-reduced-motion`: CSS already slows animations — verify; add a
+   static fallback for the dots if needed.
+6. Server: confirm the per-turn log line includes `embed_ms` and
+   `total_ms` (add if Phase 03 omitted it).
+
+## UI Verification
+Walk the full state machine by hand (dev server + mock LLM slow path):
+submit → indicator + "Thinking…" disabled button → live tokens → done
+(enabled, focused input). Kill the mock mid-stream → banner + recovery.
+Contrast of disabled button + spinner OK; reduced-motion pass.
+
+## Testing & Quality
+- Unit/integration: SSE error event serialization; timeout constant
+  exported/testable; (JS logic is E2E-covered).
+- Coverage: **>90%** on `app/`.
+
+## Playwright Execution Phase
+Run ONLY this story's suite:
+
+```bash
+uv run pytest tests/e2e/test_loading_feedback.py -v --no-cov
+```
+
+Implements the story mapping (mock LLM's 3s "pretend to think slowly"
+warm-up + a fixture that stops the mock): typing indicator visible during
+pre-token and gone by answer; button disabled→"Thinking…"→enabled "Send";
+streaming appends (two-timestamp length check); LLM-down ⇒ `role=alert`
+banner + button recovered.
+
+## Success criteria
+- [ ] every in-flight state has a visible indicator; button never zombies
+- [ ] error + 120s timeout paths both recover cleanly
+- [ ] reduced-motion respected
+- [ ] unit + integration green, coverage >90%
+- [ ] story E2E green in isolation
+- [ ] committed
+
+## Commit
+```bash
+git add -A && git commit --no-gpg-sign -m "feat(ui): explicit chat state machine — typing indicator, streaming progress, timeout and error recovery"
+```