spec-firstlisted

# Spec First Without an external contract, the agent drifts after ~3 iterations — and the failure looks like progress (code written, tests pass, wrong goal solved). Write `PROMPT.md` BEFORE acting: - **Goal** — one sentence. - **Done when** — concrete, checkable conditions. "Test suite green: <cmd>". - **Never touch** — files/areas off-limits. - **Stop if** — more than N files outside scope change; a passing test starts failing. The agent re-reads this file every iteration. State (what's done) goes in a separate `IMPLEMENTATION_PLAN.md` it updates in place. If you can't write "done when" concretely, the task isn't ready — clarify before coding.