/start-task: build a task

1. Load context: AGENTS.md, the task file docs/tasks/<id>-*.md, and only the docs/ADRs/feature specs it links. Check that its dependencies are done. If not, stop and say so.
2. Confirm the plan: restate the goal, scope, and approach in a few lines. If anything in the spec is ambiguous or needs a design decision, ask the owner first. A real decision gets an ADR (/adr).
3. Set the status to in-progress (task file + board).
4. Implement within scope only. Put unrelated findings in the inbox (/idea), not in the diff.
5. Test: add or adjust tests per the test plan, and run the test, lint, and type commands from AGENTS.md.
6. Review: run the design-reviewer agent on the change and fix what it finds (or explain why not).
7. Definition of Done: go through docs/process/definition-of-done.md, updating docs and specs as needed.
8. Set the status to review. Give a summary: what changed, how it was tested, anything left open.
9. Stop. Don't commit or push. The owner reviews first. Offer /handoff.