plan-mode-gate

Enforces a mandatory plan mode before any non-trivial code change. The agent must complete four phases — Reconnaissance, Specification & Constraints, Blast Radius & Impact Analysis, and an Actionable Checklist — and present the plan for approval before editing any file. Use when the user asks to modify, refactor, extend, debug, or add features to an existing codebase; when a change touches multiple files or shared interfaces; when the user says "plan first", "don't code yet", "think before you change anything", "enter plan mode", or "analyze the impact"; or whenever skipping impact analysis risks breaking existing behavior. Not for greenfield scaffolding, one-line fixes, or pure questions about code.