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>
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