Driver Implement

<!-- Orchestrator contract:
  role: driver
  reads: [PLAN.md, TASK_QUEUE.md, NOW.md, DIFF_SUMMARY.md]
  writes: [TASK_QUEUE.md, NOW.md, DIFF_SUMMARY.md, PROOF.md, DESIGN_BREAK.md]
  never_writes: [REVIEW_NOTES.md, DIFF_REVIEW_NOTES.md, REREVIEW_NOTES.md]
  produces: [STEP_RESULT.json]
-->
# 3. Driver — Implement

You are in Driver mode.

Bootstrap: follow Driver Bootstrap in AGENTS.md.
Resolve active slice from ROADMAP as `changes/<slug>/`.

Goal:
Execute current slice tasks from NOW/TASK_QUEUE, keep diffs small, and persist progress.

Rules:
- Follow Design Freeze from PLAN.
- If structure-changing issue appears:
  - stop implementation
  - append `DESIGN_BREAK.md`
  - do not self-approve design change
- Keep NOW at max 3 tasks.
- Update TASK_QUEUE statuses continuously.
- Append DIFF_SUMMARY and PROOF for verification runs.

Execution:
1) Execute NOW tasks in order.
2) Move task statuses + proof notes in TASK_QUEUE.
3) Refill NOW from READY tasks when appropriate.
4) Run verification commands from PLAN at checkpoints.
5) Append DIFF_SUMMARY and PROOF.

Completion decision:
- `tasks_remaining=true` if any READY/IN_PROGRESS items remain.
- `design_break=true` if DESIGN_BREAK was created/updated this run.

Output checklist:
- [ ] `changes/<slug>/TASK_QUEUE.md` updated
- [ ] `changes/<slug>/NOW.md` updated
- [ ] `changes/<slug>/DIFF_SUMMARY.md` appended
- [ ] `changes/<slug>/PROOF.md` appended
- [ ] `changes/<slug>/DESIGN_BREAK.md` appended only if needed
- [ ] `changes/<slug>/STEP_RESULT.json` written

## STEP_RESULT.json (required)