fix(streaming): move error event handling before thread.* check

[C1-BA-B1-F3]

Problem

The error event check inside the block in is unreachable because never starts with . This means error events from the SSE stream are silently ignored in the thread event path, instead of raising an .

This is a regression from commit ("fix(streaming): correct indentation").

Fix

Move error event handling to the top of the event loop, before the check, so error events are always handled regardless of context.

Before (unreachable code):

if sse.event and sse.event.startswith("thread."):
    data = sse.json()
    
    if sse.event == "error" and is_mapping(data) and data.get("error"):  # NEVER TRUE!
        raise APIError(...)
    
    yield process_data(...)

After (error events handled first):

if sse.event == "error":  # Handle error events first
    data = sse.json()
    if is_mapping(data) and data.get("error"):
        raise APIError(...)
    raise APIError(...)  # Always raise on error events

if sse.event and sse.event.startswith("thread."):
    data = sse.json()
    yield process_data(...)

Changes

• : Move error event handling before check in both and
• : Add tests for error event handling

Fixes #2796

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve assistant error events

When Assistants streams emit event: error, the payload is the top-level ErrorObject used by AssistantStreamEvent.ErrorEvent, and the assistant stream handlers still have an event.event == "error" branch. This unconditional fallback now raises APIError for that valid event shape because it lacks a nested error key, so consumers of Stream[AssistantStreamEvent]/the assistant helpers can no longer receive the typed error event; the async block has the same behavior.

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