[BUG] Misleading error message when command frontmatter specifies invalid 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?

When a custom command (.claude/commands/) has an invalid model value in its frontmatter,
Claude Code shows this error:

> There's an issue with the selected model (claude-fake-model). It may not exist or you may
> not have access to it. Run /model to pick a different model.

The hint "Run /model to pick a different model" is misleading — the session model is perfectly
valid. The problem is in the command's frontmatter, not the session.

What Should Happen?

## Expected behavior

The error should clarify that the invalid model is specified in the command's frontmatter, e.g.:

> The model "invalid-model" specified in this command's frontmatter does not exist or you
> do not have access to it. Update the command's frontmatter to fix this.

## Actual behavior

The error points the user to /model, implying their session model is wrong.

Error Messages/Logs

Steps to Reproduce

1. Create a command file ~/.claude/commands/test.md with frontmatter model: invalid-model
2. Invoke the command with /test
3. Observe the error message

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.80

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Xterm

Additional Information

_No response_