fix(streaming): skip empty SSE data events and move error-event check out of thread. block

[s-zx]

Summary

Two related bugs in Stream.__stream__ and AsyncStream.__stream__ (src/openai/_streaming.py), both sync and async paths.

Bug 1: JSONDecodeError on meta-only SSE events (closes #2722)

The SSE specification allows events that carry only meta-fields (retry:, id:, event:) with no data field. The SDK's SSE parser correctly handles these by setting data = "", but __stream__ called sse.json() unconditionally:

data = sse.json()   # JSONDecodeError when sse.data == ""

This crashes with JSONDecodeError: Expecting value: line 1 column 1 (char 0) when any API gateway or proxy injects an SSE retry: directive.

Fix: skip events whose data field is empty or whitespace before any JSON parsing.

Bug 2: Unreachable sse.event == "error" check (closes #2796)

The error-event guard was nested inside the if sse.event.startswith("thread.") branch:

if sse.event and sse.event.startswith("thread."):
    data = sse.json()
    if sse.event == "error" and ...:   # ← DEAD CODE: "error" never starts with "thread."
        raise APIError(...)

Since "error" does not start with "thread.", this check can never be true — it's dead code and was a regression from commit abc25966. The error-event handling belongs in the else branch (non-thread events).

Fix: move the sse.event == "error" guard to the else branch.

Changes

• src/openai/_streaming.py — sync Stream.__stream__ and async AsyncStream.__stream__
  • Add guard: if not sse.data or not sse.data.strip(): continue
  • Relocate sse.event == "error" check from thread. block to else block