TheChoiceIsMadeOnce_OffTheCallersThread failed on CI with the code doing the right thing. It
compared the probe's managed thread id with the test's, but the test runs on a pool thread, and that
same thread is free to pick up the queued probe as soon as the test awaits.
The probe now waits on a release the test only gives once construction has returned. A probe run on
the constructing thread could never be released, and the test fails after ten seconds instead of
passing by luck. Twenty runs pass; an inline probe fails it.