Create the plan artifact (plan.md + checks.yaml executable acceptance checks) in `.agent/{branch}/` from the current conversation context. Captures all Phase 0-1 discussion into a structured, self-contained document that enables context recovery and session handoff. On every invocation, writes plan.
Create the plan artifact (plan.md + checks.yaml executable acceptance checks) in `.agent/{branch}/` from the current conversation context. Captures all Phase 0-1 discussion into a structured, self-contained document that enables context recovery and session handoff. On every invocation, writes plan.md and re-derives checks.yaml from the Acceptance Criteria; an immutable plan.vN.md snapshot is writ