One stalled DNS family or a cancelled WebSocket upgrade could keep a connection attempt alive. Push channels also stayed exhausted after the app returned to the foreground.
Race address families independently, own connection tasks through upgrade handoff, and rearm exhausted push channels on a genuine foreground resume.
Cancelling a WebSocket connect (deadline, stop, dispose, a newer attempt)
only dropped or timed out a future: the shared never-closed HttpClient kept
the address race and TLS handshake alive, and once SecureSocket.secure had
detached the raw socket even a real task cancel was a no-op, so after
ClientHello the peer stayed open and the connect future never settled.
The happy-eyeballs task now owns the transport through the TLS handoff:
cancel is idempotent, settles the task at once, destroys an undelivered raw
winner, and destroys whatever a handshake in flight eventually yields. Each
WebSocket upgrade runs on its own HttpClient inside a connection attempt
with completion plus cancellation; the library-event, companion-remote and
Watch Together relay sockets cancel it on stop, disposal, deadline and
supersession. dart:io offers no handle to abort an in-flight handshake, so
a black-holed ClientHello closes when the handshake settles, not at cancel.
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