oh my... that's embarrassing...
You are obviously right and that is the cause for the failure.
I swear I've look at the log a number of times and totally missed that!
Suggestion for a future enhancement (very handy for dumbs like me) highlight the build error messages with a red colour. It can be difficult to spot those, specially in logs with hundreds of thousands lines on which the error doesn't spot the build immediately and, therefore, the root cause is not right at the very end of the log output.