Cancelled handshakes can remain in transport state after their application
owners return. Waiting for client idleness before signaling endpoint stop
added a measured three-second grace timeout to shutdown.
Stop and join the owned endpoint directly after application scopes drain.
Keep supervisor joining and isolated runtime teardown, which also finish
s2n's adapter workers and release their socket clones. Use this normal cleanup
for rejected-handshake tests instead of their former special shutdown path.
Test Plan:
- A loopback silent-peer handshake reproduced a 3.001-second wait before the fix.
- New supervisor regression verifies wait_stopped completes within one second
and releases the client UDP socket after cancelling an in-flight handshake.
- just test: all 796 workspace tests passed, including the new regression.
- just fmt and just clippy: passed.
- Actual native window-close timing was not manually measured.
ddidderr
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