[BUG] While in planning mode model command tricks agent into thinking it's running Haiku but it is not

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?

While in planning mode use the /model command to switch to Haiku.
It fails to switch and now thinks it's using the Haiku model even though it is on Sonnet.

What Should Happen?

I know Haiku is not compatible with planning mode but the agent should inform the user that it was unable to swap to Haiku and that it is still on Sonnet.

Error Messages/Logs

Steps to Reproduce

Open claude
Shift+Tab into planning mode
/model
select Haiku & Press Enter

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v2.1.141

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

<img width="1411" height="268" alt="Image" src="https://github.com/user-attachments/assets/3e869f0e-6fc1-447f-b50e-3cf7f4dddef3" />