The 64 KiB inter-event SSE sanitize buffer added in #96989 rejects a single
legitimate event larger than 64 KiB — e.g. a large gpt-5.5 reasoning summary on
the openai-chatgpt-responses API — throwing "SSE response exceeded max buffer
size (65536 bytes) without event boundary" and failing the whole request. The
default ChatGPT-subscription gpt-5.5 path is unusable (present in v2026.6.11-beta.1).
Decouple the two bounds: keep the non-OK error-body cap tight at 64 KiB
(SSE_NONOK_BODY_MAX_BYTES), and raise the inter-event sanitize buffer to the same
16 MiB ceiling as the JSON-synthesis path. The guard still trips on a genuinely
boundary-less (hostile/broken) stream, just not on a real large event.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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