Is there a way to get all message types have been scanned and “added” to Bus after endpoint startup?
It depends highly on the version of NServiceBus you’re using. It’s never really been a first-class feature.
There’s a class MessageMetadataRegistry which I believe is added to the container. In some versions I believe it was internal so you had to do some funky reflection to get at the data, but in the latest version, it looks like it’s public and you could just interrogate it directly.
Does that help?