Coprocessor with streaming responses panics when supergraph_response is configured

[BrynCooke]

The logic for supporting deferred responses can't work.

The issues is here:

router/apollo-router/src/plugins/coprocessor/supergraph.rs

Lines 431 to 432 in cf4a79a

	let payload = Externalizable::router_builder()
	.stage(PipelineStep::SupergraphResponse)

.

This will always panic as the wrong builder is used for the stage

Reproduction
Configure coprocessor.supergraph.response in router.yaml, for instance:

coprocessor:
  supergraph: 
    response:
      body: true

Send a query to the router that uses @defer
Router will panic.

Mitigation
Anyone who is using a coprocessor with coprocessor.supergraph.response configured should explicitly disable defer and not use subscriptions.
OR
Disable coprocessor.supergraph.response

[garypen]

I think your description is wrong in the issue. It's supergraph logic that is mistakenly using a router builder, so the impact is on the new supergraph coprocessor.

It should be:

Reproduction
Configure coprocessor.supergraph_response
Send a query to the router that uses @defer
Router will panic.

Mitigation
Anyone who is using a coprocessor with supergraph_response configured should explicitly disable defer and not use subscriptions.
OR
Disable coprocessor supergraph_response

[BrynCooke]

You are right, I've updated it.

[o0Ignition0o]

#3647 is when the bug was introduced, so router [1.31.0..=1.32.0] are affected