poll() can report Phase.DONE for a ticket before the whenComplete hook that
stamps Task.completedNanos has run — CompletableFuture.complete() publishes
its result and only then runs dependents. The TTL tests advanced an injected
clock right after observing DONE, so on a host where the hook runs late it
stamps the ADVANCED time and the eviction never happens (fails on Linux,
passes on macOS).
Add a package-private test seam, MessageService.isCompletionStampedForTest,
that reports whether completedNanos is stamped. Both TTL tests now wait on
that (a real volatile read/write happens-before edge) before advancing the
clock, instead of on Phase.DONE. The prune condition in pruneTerminalTickets
is untouched.
Dai Ha