Create Plan Artifact

Generate .agent/{branch-name}/plan.md — the single source of truth for autonomous execution — alongside an immutable plan.vN.md snapshot of the same content.

A new Claude session MUST be able to execute from plan.md alone without the original conversation.

Every plan iteration produces a new plan.vN.md snapshot. plan.md always points at the latest version; plan.v1.md, plan.v2.md, … are immutable history.

Prerequisites

Before invoking this skill:

1. Phase 0 (Validation) must be complete — requirements confirmed with user
2. Phase 1 (Planning) must be complete — codebase analyzed, decisions made
3. Confidence gate should have passed (90%+ on plan mode)
4. A worktree must exist — plan.md is created INSIDE the worktree, never on main