* fix(api): Responses passthrough emits event-only SSE frames after filtering commentary output (#6561)
The #6199 commentary-drop `continue;` branches in stream.ts skipped the
data: line for a dropped commentary event but never cleared the
already-buffered event: line for the same frame, so the next blank line
flushed the stale event: line alone -- an event-only SSE frame that
crashes the OpenAI Python SDK's json.loads(). Both drop sites now call
clearPendingPassthroughEvent() before continue. The commentary-drop
decision was extracted into a new responsesCommentaryDrop.ts module so
the fix does not grow the frozen stream.ts.
* chore(6735): re-sync onto release tip; CHANGELOG entry → changelog.d fragment (fragments-first)
