Fix error when streaming from Gemini includes only executable_code or code_execution_result

[binaryCrossEntropy]

Gemini models (google-genai >= 1.31.0) can emit streaming parts that only
contain executable_code or code_execution_result with no text. Our
streaming handler asserted on these parts, causing an AssertionError.

This change:

• Ignores chunks that only have executable_code or code_execution_result
• Mirrors existing behavior for Anthropic/OpenAI where similar built-in
  tool calls are skipped during streaming
• Prevents AssertionError when combining Gemini streaming with
  CodeExecutionTool

Closes #2626 #2626

[DouweM]

@binaryCrossEntropy Thank you! Can you see if you can add a test that triggers this code path? Likely just using the code execution built-in tool will do it.

[binaryCrossEntropy]

Hiya @DouweM - I’ve added a test that triggers the path where Gemini streams executable_code / code_execution_result.
I put my test case in tests/models/test_google.py and also added a cassette file.

Files modified/added:

• Test: tests/models/test_google.py::test_google_model_builtin_code_execution_stream

• Cassette: tests/fixtures/cassettes/test_google_model_builtin_code_execution_stream.yaml

The test passes with this fix, and it fails with an AssertionError if I remove the code.

(ignore the function name I modified it later)

Test pass:

Happy to work on other feedback :)

[DouweM]

@binaryCrossEntropy Thanks Iqbal!