Malformed XML-like `TextBlock` response instead of `ToolUseBlock` with Batch API

[gordonhart]

Seeing an issue with tool use in the Batch API this afternoon. When forcing tool use with tool_choice=dict(type="auto") or tool_choice=dict(type="tool", name="my_tool_name"), the API is returning a TextBlock with content like this (tool name and parameter names replaced with placeholders):

="my_tool_name">
<parameter name="example_parameter">lorem ipsum</parameter>
<parameter name="example_parameter_2">lorem ipsum</parameter>
<parameter name="example_parameter_3">[]</parameter>
</invoke>
</function_calls>

The tool name is correct, the parameter names are correct, and the parameter values are correct for the requested tool. However, rather than having this shaped nicely into a ToolUseBlock with name and input set accordingly, it's yielded as a broken XML string. The rest of the MessageBatchIndividualResponse looks correct.

Only seeing this with the Batch API, and only started seeing this in the past hour or so.

[gordonhart]

Seeing this from the synchronous API occasionally now as well.