fix(streaming): remove unreachable sse.event == error check

[Mr-Neutr0n]

Summary

Fixes dead code bug where the sse.event == "error" condition was unreachable.

Problem

The sse.event == "error" check was nested inside a block that requires sse.event.startswith("thread."):

if sse.event and sse.event.startswith("thread."):
    data = sse.json()
    if sse.event == "error" and is_mapping(data) and data.get("error"):  # Always False!
        raise APIError(...)

Since "error" does not start with "thread.", this condition can never be True.

Solution

Changed the check to look for error data in the payload rather than the event name:

if sse.event and sse.event.startswith("thread."):
    data = sse.json()
    if is_mapping(data) and data.get("error"):  # Now works!
        raise APIError(...)

This is consistent with how errors are handled in the else branch for non-thread events (lines 84-96).

Changes

• src/openai/_streaming.py: Fixed both sync (line 67) and async (line 170) versions

Test Plan

• Syntax validation passes
• Logic now allows error detection for thread.* events by checking the data payload

Fixes #2796

[Mr-Neutr0n]

Friendly follow-up - is there anything I can improve in this PR? Happy to address any feedback.