When emitting responses by value, the channel emitter should convert to a pointer

The http emitter does this automatically because we're serializing but the channel one doesn't. We could also assert the correct type but I'd actually just rather DWIM.

Start at the channel emitter and compare its response handling with the HTTP emitter, which already converts values during serialization. Confirm how value responses are emitted and make the channel path convert them to pointers; done means channel-emitted responses behave consistently with HTTP responses.

Written by the indexing model from the issue text.