[FEATURE] /implement command to clear context and start implementation from a plan file

Problem Statement

Plan Mode's best feature is its exit transition: "Clear context and implement the plan?" — it drops context from ~80% to ~20-30% and auto-loads the plan file as the implementation guide. But this transition is only available when exiting Plan Mode.

Users who write plan files through other means (skills, custom workflows, direct creation) have no way to trigger this transition. They must manually /compact, then tell Claude to read and implement the plan — a fragile, multi-step workaround.

Current behavior

After writing a plan file outside Plan Mode:

Plan updated at .claude/plans/my-plan.md.

No transition offered. User must:

1. /compact manually
2. Tell Claude: "read .claude/plans/my-plan.md and implement it"
3. Hope compact preserved enough context about which plan to use

Proposed solution

A /implement command that replicates Plan Mode's exit transition for any plan file:

/implement .claude/plans/my-plan.md

Or with auto-detection of the most recently modified plan:

/implement

This would:

1. Show the plan content for review (like Plan Mode does)
2. Offer the same options: clear context + bypass permissions, preserve context, manually approve, etc.
3. Clear context and load the plan as implementation guide

Essentially: Plan Mode's exit flow, without requiring Plan Mode's entry.

Why this matters

The plan → compact → implement cycle is the most natural workflow for complex tasks. Plan Mode nails the transition but forces you to use its built-in planning. A standalone /implement command decouples the transition from the planning method, letting users plan however they want and still get efficient context management.

Related issues

• #6207 — Persistent Plan Storage (plans lost after compact)
• #27955 — Auto-compact loses plan context
• #19326 — Compact option when exiting plan mode

Environment

• Platform: darwin
• Version: latest