A failed request is reported even when a module is incomplete

When a request could not be delivered, the hub tells the sender so — that failure notice is how a save, a create, or a page knows to show an error instead of waiting forever.

Writing that notice runs the same serializer as every other message, and the serializer runs a small diagnostic: it looks through the assembly of the type it is serializing for related types nobody registered, so it can warn about them. When a package shipped without one of its dependencies, that look-through failed — and its failure escaped and took the failure notice with it. The sender never heard back. On the affected portals this looked like requests that neither succeeded nor failed, with a single "breaking error cascade" line in the log as the only trace.

The diagnostic now stays a diagnostic. It reports what it could not load — once per assembly, with the assembly's name and the dependency it is missing — and the message it was serializing goes out regardless. The incomplete package is still a defect (and is fixed separately), but it can no longer silence the report of some other request's failure.