Depends on D18845. See PHI243 for context and more details.
Briefly, some objects need a "type" transaction (or something similar) very early on, and we can't generate their fields until we know the object type. Drydock blueprints are an example: a blueprint's fields depend on the blueprint's type.
In web interfaces, the workflow just forces the user to select a type first. For Conduit workflows, I think the cleanest approach is to proactively extract and apply type information before processing the request. This will make the implementation a little messier, but the API cleaner.
An alternative is to add more fields to the API, like a "type" field. This makes the implementation cleaner, but the API messier. I think we're better off favoring a cleaner API here.
This change just makes it possible for DrydockBlueprintEditEngine to look at the incoming transactions and extract a "type"; it doesn't actually change any behavior.