# Phase 15 — Tune How Brain Answers (Steering Notes)

**Story:** `.agent/user_stories/steering-notes.md`
**Context:** owner report 2026-08-22 — "the answers are off. Add a
feature that lets me 'tune' the output if I think an answer isn't quite
right. This tuning should be added to the database and read in with the
system prompt to steer the replies."

## Goal
A first-class **steering** loop: under any answer, "Tune" → short
instruction → stored in Postgres (`steering_notes`) → injected into the
system prompt of **every** subsequent turn → observable in the reply.
Notes are listed and deletable in a "Tuning" panel.

## Implementation steps
1. **Schema** — `alembic/versions/0003_steering_notes.py`:
   `steering_notes(id UUID PK, note TEXT NOT NULL, created_at
   TIMESTAMPTZ NOT NULL DEFAULT now())`; downgrade drops the table.
   Model `SteeringNote` in `app/models.py`.
2. **API** — `app/api/steering.py` (stateless, A10):
   - `GET /api/steering` → `{notes: [{id, note, created_at}]}` newest
     first.
   - `POST /api/steering` `{note}` (trimmed, 1–2000 chars; 422 on
     empty/over-long) → 201 with the created note.
   - `DELETE /api/steering/{note_id}` → 204; 404 unknown id.
   Mount in `app/main.py`; schemas in `app/schemas.py`.
3. **Prompt** (`app/rag/prompts.py`):
   - `build_steering_section(notes: Sequence[str]) -> str` — `""` when
     empty; else `<tuning>…</tuning>` with numbered notes, capped at
     `steering_max_chars` (new setting, default 8000; `[…truncated…]`
     marker). **Both** HIGH and DEFLECT prompts carry it (after
     `<relevance>…</relevance>`, before `<documents>`/DEFLECT_MODE
     body). With zero notes the prompt is byte-identical to today.
   - Preserve the owner's working-tree persona edits (no "you've got
     this" / no mandated deflection opening — align
     `tests/unit/test_prompts.py` verbatim check with the current text;
     record as a PLAN §6 revision).
4. **Chat turn** (`app/api/chat.py`): load notes (created_at asc),
   pass into `plan_turn` → prompts; per-turn log line gains
   `tuning=N` (PLAN §9).
5. **E2E mock** (`tests/e2e/mock_llm.py`): when the system prompt
   contains `<tuning>`, the composed answer ends with
   ` (tuning: <first note line>)` — makes prompt injection observable
   in the UI deterministically.
6. **UI** (`frontend/index.html`, `app.js`, `styles.css`):
   - "Tune" button (`.tune-btn`, ghost, ≥44px) in the meta row of every
     completed brain bubble (deflected included).
   - Inline `.tune-form`: labeled textarea (maxlength 2000) + Save /
     Cancel → `POST /api/steering` → success `.tune-saved`
     (role=status: "Saved — future answers will follow this.") or
     inline error (role=alert), form kept on failure.
   - Header `#steering-toggle` "Tuning" + count badge; `#steering-panel`
     (region) above the messages: notes newest-first, per-note delete
     (labeled); empty text; count updates on add/delete.
   - a11y: aria-expanded/controls on the toggle, aria-live announcements
     for save/delete, focus-visible, Phase-08 tokens (all ≥4.5:1).
7. **Docs:** README "Tuning your answers" section; PLAN §4/§5/§6/§9/§7.5
   + roadmap rows 11–15.

## Locked decisions
None broken: A10 (stateless endpoints), A13 (alembic), A16 (one E2E
suite), A11 (no library). New table + new setting only.

## Testing & Quality
- **Unit:** steering section (empty/one/many/budget truncation), prompt
  placement in both modes, persona-verbatim check aligned to the
  owner's current persona.
- **Integration:** steering CRUD (201/200/204/404/422, ordering,
  validation); chat turn with a stored note → fake LLM's captured system
  prompt contains the note (HIGH **and** LOW); log line `tuning=N`.
- **Coverage:** `uv run pytest --cov=app --cov-report=term-missing`
  **>90%**.
- **E2E:** `tests/e2e/test_steering.py` per the story mapping.
- **Regression:** `test_chat_rag.py`, `test_honest_deflection.py`,
  `test_retrieval_quality.py` green in isolation (zero-note prompt is
  byte-identical, so behavior is unchanged until a note exists).

## Commit
```bash
git add -A .agent/ alembic/ app/ frontend/ tests/ README.md && git commit --no-gpg-sign -m "feat(rag): steering notes — tune how Brain answers, stored in Postgres and injected into every system prompt"
```