A publish that fails after the cancel now ends in CancelledError (after
its prune) instead of a 500, and the restored library is adopted to its
end even when a second cancel arrives. The blocking calls go through
_run_in_executor again, as the executor contract test expects.
Exit-window refusals: the comments state what was measured (a pool is
refused during threading._shutdown; Thread.start only once the
interpreter is finalizing), and the tests assert the one DEBUG line.
Vito Sansevero
b5b643ba7a