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Server-Sent Events: CORS with EventSource, credentials mode, and custom fetch wrappers for POST-based SSE
`EventSource` is GET-only and follows CORS rules for long-lived streams—custom POST SSE needs explicit CORS on every chunk.
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ssecorsstreaming
HTTP/2 multiplexing
SSE streams can starve other requests on the same connection—use separate connection coalescing policies.
HTTP/3 QUIC changes packet loss behavior—monitor end-to-end latency separate from CORS.
Caching
CDN caching of SSE responses is almost always wrong—use `Cache-Control: no-store` on streams.
Reverse proxies may buffer—disable buffering for `text/event-stream`.