Plan from previous session auto-injected and executed in new session

Bug Description

When a Plan Mode session ends (ExitPlanMode), the plan content is persisted. Upon starting a new session, Claude Code automatically injects the previous plan as a prompt ("Implement the following plan: ...") and begins executing it — even if the implementation was already completed and committed in the previous session.

Steps to Reproduce

1. Enter Plan Mode, create a plan, then exit Plan Mode (ExitPlanMode)
2. Complete the implementation (code written + committed)
3. Start a new conversation/session
4. Claude Code automatically injects the old plan and starts executing it

Expected Behavior

A new session should not automatically resume or execute plans from a previous session without explicit user instruction.

Actual Behavior

The previous plan is injected as "Implement the following plan: [plan content]" at the start of the new session, and Claude Code proceeds to execute it autonomously.

Impact

Low severity (no destructive behavior observed — code already existed, no files were overwritten). However, it wastes tokens and could be dangerous if the plan involved destructive operations.