The 5-minute session-sweep interval at sessionTimeout.js:17 fired at
module-load time without .unref(), so every jest worker that
transitively required this module (server.js → middleware → most
of the route layer) kept the event loop alive forever. The worker
then got force-killed on shutdown, surfacing as the longstanding
"worker failed to exit gracefully" warning at the end of every CI
run on upstream/beta.
Under enough I/O / memory pressure on a CI runner, the force-kill
could land MID-test rather than after the suite finished, taking
out whatever else was running on that worker — most visibly
integration/storageBackend.test.js on PR #555's runs.
.unref() makes the timer not keep the loop alive on its own.
Production behaviour is unchanged: the timer still fires every
5 min as long as anything else is holding the loop open (the HTTP
server, always).
Luca
ecb2aeacf9