What is the proper way to intercept tool calls modify them or dynamically approve/reject them?

I created a tiny sample: provided a session with a tiny tool to tell the date and time to the model. Asked the model to stream response to "What time is it" and just get this error: The operation couldn’t be completed. (FoundationModels.LanguageModelError error -1.) There is no relevant output on Xcode console. And profiling with the new Foundation Models instrument brings zero more insight into the issue. I know it could be many things, but it there may be more information the tools could surface in debug?

The LanguageModelSession.GenerationErrors seems to be deprecated in favor of LanguageModelError for the most part. Now... when iterating through the ResponseStream<String> of a LanguageModelSession.streamResponse(to:options:), with a good old for await, the async iterator .next() can throws. Leaving aside that it is not very conspicuous at the call site it will throw... in the do/catch, the error thrown does not see to be able to be pattern matched to the new LanguageModelError with something like catch let error as LanguageModelError. It was able to patten match the GenerationErrors before just fine, so may be an oversight/bug?