Agent seems unable to exit Plan mode

### Short summary

Agent had to be forced out of planning mode with multiple prompts

### Affected version or release

v1.1.6

### Installation context

Windows

### What happened?

I have two threads where the initial prompt was in planning mode.
Following the planning, it was almost impossible to make the agent perform work.

### Steps to reproduce

1. Start prompt in planning mode
2. Accept the plan and start implementing in Interactive or Autopilot mode
3. The agent had to be told multiple times to actually do the actions

### Expected behavior

Agent starts working once the plan is accepted and mode is changed from Plan to Interactive or Autopilot

### Additional context

Windows で v1.1.6 を使用し、Plan モードで開始してプランを承認し、Interactive または Autopilot に切り替えることで問題を再現します。エージェントが繰り返しプロンプトを表示しなくても作業の実行を開始するかを比較します。モード遷移によって確実に実装が開始されれば完了です。

索引モデルが issue の本文から書いたものです。