Live SSE frames for a phase:"commentary" message were already dropped
per #6199, but the terminal response.completed.response.output array was
forwarded verbatim whenever the upstream echoed the same item back
non-empty, since backfillResponsesCompletedOutput only fills an empty
array. Reuse the existing isResponsesCommentaryMessageItem predicate to
filter the terminal snapshot's output array (and, defensively, the
backfill buffer it can be seeded from) so both representations agree.
Regression test added to tests/unit/responses-commentary-passthrough-6199.test.ts
reproducing the exact upstream shape from the issue.
Reworks stream readiness as a ping/zombie filter instead of a semantic content
gate: downstream streaming is released as soon as any structured non-ping SSE
event arrives, replaying the buffered prefix. Removes the fixed 2s first-byte
cap (readiness now inherits REQUEST_TIMEOUT_MS unless STREAM_READINESS_TIMEOUT_MS
is set) so slow first-byte reasoning providers no longer false-504.
Combo stream quality stays strict: validateResponseQuality still requires an
actual content_block / known non-Claude payload before accepting a routed target.
Also normalizes multi-line data: framing, metadata-prefixed events, and final
events that arrive without a trailing blank line.
Integrated into release/v3.8.25.
Co-authored-by: R.D. <rogerproself@gmail.com>
