Peek the first SSE frame in wrapQoderSSE; if statusCodeValue != 200 and the
body carries a billing signature (code 112/10605 or pricingUrl), return a
synthetic 403 so chatCore marks the connection unavailable and triggers
combo/account fallback instead of leaking the error text into chat.
wrapQoderSSE becomes async; consumed peek bytes are re-processed in the
stream start() seed loop so nothing is dropped.
