Ref T11887. This isn't a great fix but makes the method behave properly until I get around to a real fix.
In the longer term, I want to convert all of this pluggable Harbormaster/Drydock stuff (blueprints, artifacts, build plans) to use EditEngine + EditField instead of the weird mishmash of older/custom stuff it currently uses. However, this is a more involved project to execute and I'd like to be in that area of the codebase first so it gets adequate testing.
Until that happens, just put a reasonble-ish mechanism in place to let artifacts correct inbound types. This is the only artifact type and only parameter which needs casting.