Transports & Subscriptions

Because a browser's WebSocket API gives page JavaScript no way to send or observe the transport's own liveness probe. The subprotocol therefore defines ping and pong as ordinary JSON messages that either side may send, carrying no operation id.

Only when the deferred part is measurably slower than the rest and the interface can render usefully without it. If the client blocks on the whole tree, or the slow field is what the screen exists to show, deferring adds payloads and merge logic and moves nothing.

Failures that used to answer 200 start answering 4xx, so client and infrastructure code keyed on the status takes a different branch. The GraphQL over HTTP draft makes the choice Accept-driven, so a server answers the newer type only to clients that asked.

Because the unit the infrastructure sees is the batch, not the operation. One composite POST body means one cache key, one status, one access-log line and one span, so hit rates, error rates and latency can no longer be attributed to individual operations.

Budget in executions per second, not sockets: peak subscribers on the hottest single entity times that entity's event rate, times the CPU and backend calls one execution costs. Then decide whether the feature can afford that.