implementation-plan

Create structured implementation plans for complex features, refactoring, or multi-phase work. MUST be used when user asks to "create a plan" or "make an implementation plan" or work requires multiple distinct phases. Creates file named IMPLEMENTATION_PLAN_<feature-name>.md with phases that include tasks, quality gates (code review, tests, linter, type checker), and status tracking. Each phase must have Goal, Status (Not Started/In Progress/Complete), Tasks checklist, and Quality Gates checklist. Plans are living documents - update as work progresses, commit with code changes.