[BUG] Fable 5.1 - The configured advisor model is not compatible with this request model

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?

Upon upgrading to 2.1.257 and changing my model to Fable 5.1 I noticed that the advisor model also migrated to 5.1 with no option to go back to 5.

In a conversation from before the upgrade, which was using a Fable 5 Advisor I now see this whenever advisor is enabled

● API Error: {"type":"error","error":{"type":"invalid_request_error","message":"tools.24.model: 'claude-fable-5' cannot be used as an advisor when the request model is
  'claude-fable-5-1'."},"request_id":"req_011CedBCqDRKDYGLw1PPCc5C"} · The configured advisor model is not compatible with this request model — run /advisor to change or disable the advisor

What Should Happen?

The advisor process should continue working with the new advisor model, or the old one, but it should keep working rather than crash.

Error Messages/Logs

Steps to Reproduce

Taking some guesses:

• Start a conversation on <2.1.257 that has advisor setup and has used it at least once (not sure this is required)
• Upgrade to >=2.1.257
• /advisor and note you're on Fable 5.1 now
• Try and do something that makes the conversation use the advisor

Claude Model

Other

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.257

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

_No response_