Handling invalid UTF-8 bytes

I'm looking at using vte for a use case where I want to translate invalid UTF-8 bytes into Unicode replacement characters, however vte seem to silently swallow some invalid UTF-8 bytes. For example, if I feed it input consisting of the byte 0x90, it produces no events.

Would it make sense to add `Execute` rules to the `Ground` table for 0x90 and other formerly special C1 codes?

Would it make sense to introduce something like a `InvalidUtf8` action, to fill in the `Ground` table in general?