[Bug] Chat becomes unresponsive after "Prompt is too long" error

Bug Description
In the Claude Visual Studio Code extension, if the plan file or prompt is too long, it gives a "Prompt is too long" error. After this error, it continues to give the same error for everything you type in that chat. Therefore, you can no longer use the existing chat and need to start a new one.

Environment Info

• Platform: win32
• Terminal: null
• Version: 2.1.0
• Feedback ID: 5d6efac4-7bd7-4f1f-bf14-0bec408ec636

Errors

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<img width="2242" height="1487" alt="Image" src="https://github.com/user-attachments/assets/2aa625c8-e1a1-424d-8469-d0e686372926" />