fix: wrap transport failures while consuming a stream

[lazerg]

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Changes being requested

_base_client wraps failures from the initial send, but Stream and AsyncStream iterate the response body with nothing around the loop. A read timeout or a dropped connection part-way through a stream therefore surfaces as a raw httpx2.ReadTimeout or httpx2.RemoteProtocolError, so except openai.APIError around a streaming call misses the most common streaming failure.

Both stream classes now catch transport failures raised while the body is consumed and re-raise them as APITimeoutError or APIConnectionError, keeping the original exception as __cause__. transport_exceptions() sits next to the existing compat helpers in _httpx2.py, so a loaded legacy httpx is covered the same way as timeout_exceptions().

Two knock-on changes come with that. The assistants event handler decides whether to fire on_timeout() from the same exception set, so APITimeoutError was added there to keep that callback firing on a stream read timeout. And test_assistant_stream_timeout_callbacks_preserve_httpx2_family asserted the raw httpx2.ReadTimeout; it now asserts the wrapper and checks __cause__, which still pins the httpx2 family.

Raw byte streaming through with_streaming_response is untouched and still surfaces httpx exceptions directly. Whether a partly consumed stream can be retried is a separate question and is not addressed here.

Additional context & links

Closes #3811

Validation:

• 3,153 tests passed, 120 skipped, across the suite excluding tests/api_resources, tests/lib/test_fine_tuning_positional_arguments.py and tests/test_uv_workflows.py, which need the mock server or network
• test_transport_error_mid_stream covers sync and async against both a timeout and a protocol error; all four cases fail on main
• Ruff check and format, mypy, and Pyright passed
• Custom-code budget: 6,626 / 10,000 lines

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Wrap HTTP decoding failures as connection errors

When a streaming response has malformed or truncated compressed content (for example, an invalid Content-Encoding: gzip body), response.iter_bytes() raises httpx2.DecodingError. That exception is a RequestError, not a TransportError, so this handler—and the identical async handler—still exposes a raw HTTPX2 exception instead of an APIConnectionError; consequently, except openai.APIError continues to miss this stream-consumption failure even though non-streamed responses wrap it. Catch DecodingError as well, or otherwise cover the relevant request-error family.

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