[BUG] Plan files persist in ~/.claude/plans/ after completion

Description

Plan files created during plan mode accumulate in ~/.claude/plans/ and are never deleted after the plan is executed and approved.

Steps to reproduce

1. Enter plan mode (e.g., user requests a complex task)
2. Claude creates a plan file in ~/.claude/plans/ (e.g., vast-gliding-fog.md)
3. User approves the plan via ExitPlanMode
4. Claude executes the plan successfully
5. Bug: Plan file remains in ~/.claude/plans/
6. After context compaction, Claude re-reads the old completed plan
7. Claude sometimes gets confused and tries to execute the already-completed plan again

Current behavior

• Plan files accumulate indefinitely (e.g., 87 files, ~1MB after weeks of usage)
• After context compaction, Claude re-reads completed plans
• Claude may attempt to re-execute completed plans, causing confusion

Expected behavior

Plan files should be deleted (or archived) after:

1. User approves the plan AND all tasks are completed
2. Or after a configurable timeout (e.g., 7 days of inactivity)

Workaround

Manual cleanup:

# View old plans (>7 days)
find ~/.claude/plans -type f -mtime +7

# Delete old plans
find ~/.claude/plans -type f -mtime +7 -delete

Environment

• Claude Code CLI
• Linux/macOS/WSL