Function Tool verification callback before throwing "Tool xxxx is not found in the tools_dict" exception

[holance]

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Contribution guide.

Is your feature request related to a problem? Please describe.
LLM (Gemini2.5 Pro) keeps hallucinating and creates non-exist tool names. I tried to use before_tool_callback, but "Tool xxxx is not found in the tools_dict" exception is throw before this callback getting called.

Describe the solution you'd like
I would like to have another callback for tool verification before throwing this exception. Or is there any better way to handle this issue?

Describe alternatives you've considered
Need suggestions.

Additional context
None.

[jpantsjoha]

I've submitted a PR that enhances error messages for tool not found errors, which addresses the pain point described in this issue:

PR #3219: #3219

While this doesn't add a verification callback (as requested), it provides enhanced error messages with:

• Clear description of what went wrong
• List of available tools for comparison
• Possible causes (LLM hallucination, configuration error, typo)
• Suggested fixes with actionable steps
• Fuzzy matching suggestions ("Did you mean...?")

This should help developers quickly identify and resolve tool not found errors, reducing debugging time from hours to minutes.

The PR has been validated with comprehensive unit tests and addresses issues #2050, #2933, and #2164.