Plan mode shows previous plan instead of new one when switching modes mid-input

Question

When switching to plan mode while composing a new message, the plan result shown is from a previous session.

**Steps to Reproduce**
1. Start composing a message
2. Switch to plan mode mid-input
3. Submit the message
4. Old plan from previous session is shown

**Expected**: New plan based on current request
**Actual**: Cached plan from previous session is shown

```
claude --version
2.1.81 (Claude Code)
```