[BUG] Plan mode persistence causes stale context to bleed across sessions

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

## Steps to Reproduce

1. Enter plan mode in Session A, work on Task A
2. End Session A
3. Start new Session B with different Task B
4. Enter plan mode - Claude references the old plan file from Session A
5. Claude gets confused, tries to work on Task A context instead of Task B

## Expected Behavior
Each new session should start with a fresh plan file, or plan mode should prompt to clear/keep existing plans.

## Actual Behavior
The plan file (~/.claude/plans/*.md) persists indefinitely. System instructions tell Claude to "build incrementally" on stale content, polluting new sessions with old context.

What Should Happen?

## Suggested Fix

• Auto-clear plan files when starting a new session
• Or prompt user: "Found existing plan from [date]. Clear and start fresh?"
• Or scope plan files to session IDs

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce

1. Enter plan mode in Session A, work on Task A
2. End Session A
3. Start new Session B with different Task B
4. Enter plan mode - Claude references the old plan file from Session A
5. Claude gets confused, tries to work on Task A context instead of Task B

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Version: 2.0.55

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_