jaxrs api says:

• In addition to handling the standard connection loss failures, SseEventSource automatically deals with any HTTP 503 Service Unavailable responses from an SSE endpoint, that contains retry-after HTTP header with a valid value. SSE event source will automatically schedule a new reconnect attempt and use the received RETRY_AFTER HTTP header value as a one-time override of the reconnect delay.

When receive gets an inbound sse event with a valid reconnectDelay value, it should be used as one time override of the SseEventSource reconnect delay too.