Work the plan one thin slice at a time. A slice is the smallest piece that changes observable behavior.

When a spec exists at docs/specs/<slug>.md, its acceptance criteria are the plan: work criterion by criterion, and let the spec's non-goals fence every diff. A spec that still carries an ## Open decisions section is a draft, not a plan: stop and route back to drill; implementation cannot start until the draft is settled.

Follow the conventions architecture owns, loading only the ones the slice touches: the universal set indexed in architecture/conventions/ (types, failure, direction, purity, concurrency, security, observability, cohesion), FRONTEND.md for UI from a settled design, BACKEND.md for an API, service, or job, and the matching file in tooling/ for the toolchain or stack.

Pick the smallest unfinished slice of the plan.
Write the test that fails for it. Test external behavior through the interface, never implementation details. If no failing test can be written, the seam is wrong: stop and fix the plan, not the test.
Write the minimum code that makes it pass.
Refactor only with tests green. Match the existing style of the surrounding code.
Repeat until the plan has no unfinished slices.

Rules: