How are defer payloads handled in SSR initiated queries

[tgriesser]

👋 was just chatting with @benjie about some defer related things and he mentioned this is be the best forum to ask:

Are there any expectations/assumptions around how @defer is managed when a query is initiated from a server-side render? In the examples I've come across using @defer, the assumption is that the client has initiated the request and has a multipart/mixed fetch response.

If the query is server initiated via SSR or for data pre-hydration, what happens to the steam of values which is meant to be sent to the client? Are these buffered until the client is able to receive them, or are these expected to either be streamed along with the HTML response, or sent via some sort of HTTP2 push type mechanism.

Are there any situations where a defer payload could be missed due to a gap between the time they're sent by the server and the time the client is ready to receive and process them?