If you pass in false for fail fast, it disables the message, but not the behavior of short circuiting the request since the onRequestStart still returns false even if fail fast is false. I would expect setting fail fast to false to give the same behavior found in ColdBox 4 where any subsequent requests are allowed to process even though a reinit is happening. Otherwise, what is the purpose of the flag? It makes no sense to send back a white page to the user, effectively failing fast, but not actually outputting any message. We need to pick one of these:
Dev can disable fail fast and get the Coldbox 4.x behavior back, which means we need to allow the request to finish.
Or, force fail fast to always happen, which means the fail fast flag makes no sense to even have, just rename it to accept an optional closure.