I found the error (missing semi-colon after forward declaration), but what I’m more interested at this point is how to avoid the laborious line-by-line search in the future.
Does/can the UHT output any kind of log?
In my experience with UE4 (really all programming), the worst/most time consuming errors are trivially easy to fix once found (e.g. include semi-colon), but it can take literally days to find them. The biggest headaches and worst time-wasters are when one gets an exceedingly generic error without any indication of even the file that was being parsed.
In this case I got a reference to the line where the check failed, but that line encompassed a check running through the entirety of my code.