Only the platform knows the real forefront

Actually, the platform doesn't store that information either (it just uses it to put the request at the right end of the queue). And adding it to userData won't help, because list(andLock)Head doesn't return it (because it may be very large).

do not try to keep imperfect copy of it locally and rather design the system to work without being aware of the cached forefront.

I'd actually prefer to just avoid solving the problem if we're using locking.

Actually, the platform doesn't store that information either (it just uses it to put the request at the right end of the queue). And adding it to userData won't help, because list(andLock)Head doesn't return it (because it may be very large).

What is locally tracked as "forefront" is on platform the "tip" of the queue. So that is what I meant by the "Only the platform knows the real forefront"