I have a question regarding how the response protocol is determined for a request that could POTENTIALLY result in multiple payloads.

Scenario: client sends header accept: multipart/mixed with non-"Incremental Delivery" operation

Given we have an operation that does not use defer/stream at all:

query { foo }

Should the response then use the application/(graphql+)json response type or the multipart/mixed response type?

Scenario: clients sends accept: multipart/mixed, application/(graphql+)json with non-"Incremental Delivery" operation

Given we have an operation that does not use defer/stream at all:

query { foo }

Should the response then still use the application/(graphql+)json content-type or the multipart/mixed response type?
According to the current spec draft, the server should always please the order of the accept header listed content-types if possible. Would that still apply if the server is capable of serving both content-types (accept: multipart/mixed and application/(graphql+)json)

Scenario: clients sends header accept: application/(graphql+)json with "Incremental Delivery" operation

query {
  foo
  ... on Query @defer {
    bar
  }
}

Quote from current Spec Draft:

According to the HTTP 1.1 Accept specification, when a client does not include at least one supported content type in the Accept HTTP header, the server MAY choose to respond in one of several ways. The server MUST either:

Disregard the Accept header and respond with the default content type of application/graphql+json, specifying this in the Content-Type header; OR
Respond with a 406 Not Acceptable status code

Should the server in this scenario still send back multipart/mixed or raise a 406 HTTP error?

Should the fact that the client sent an operation with a defer or stream directive be a hint to the server that the client MUST be able to parse it? A client not supporting it, would probably not have requested it in the first place?

Should the server be responsible for merging the results and sending them as a single result to the client?

Should the server do the execution with the defer and stream executor functionality being disabled?

Scenario: clients sends the HTTP GET method

Is incremental delivery via GET allowed or intended?