@ConcurrencyLimit(limit=2, policy=REJECT), 4 concurrent callers, each sleeps 300ms
==================================================================================
OK in 301ms
REJECTED (InvocationRejectedException) in 0ms
OK in 300ms
REJECTED (InvocationRejectedException) in 0ms

OK: 2, REJECTED: 2 (expected 2 and 2 with limit=2, 4 callers)
Rejection throws org.springframework.resilience.InvocationRejectedException
(a RejectedExecutionException subtype) -- confirmed by javap, not documented on the annotation itself.