The Implementation Planner specialist for Headout's PM OS. Use this skill to convert an approved PRD and design into a detailed, engineer-ready (and coding-agent-ready) implementation plan. It produces a structured task breakdown with clear sequencing, per-task acceptance criteria, API contracts, state transitions, dependencies, and rollout strategy. The output of this skill is designed to be directly usable by Cursor (or any AI coding agent) as the authoritative source of truth for what to build and in what order. Trigger this skill when a PM says "write the implementation plan for this", "break this into engineering tasks", "create the tech breakdown", "what's the build plan", "prepare this for engineering handoff", or when a spec has passed L1 review and is ready for engineering pickup. The Implementation Planner requires a spec (ideally post-L1 review) as input. It can also incorporate a prototype and data insights brief if available.