Validation of function-type parameters

I expect error to occur on last line, because formal and actual signatures of callbacks do not match.
But no any warnings happened.


Start by reconstructing the callback example shown in the attached image and reproduce the missing warning for the mismatched formal and actual signatures. Trace function-type parameter validation from that reproduction; done means the final line reports the signature mismatch without introducing unrelated warnings.

Written by the indexing model from the issue text.