The SDK's DisposeAsync closes with no token, i.e. under the 30 s DefaultCallTimeout, so a
blackholed gateway parked the driver's teardown for the whole of it. CloseAsync(ct) runs the
close under the caller's token, drops the channel on a cancelled/failed close (the gateway
reaps the session on its idle lease) and leaves the session re-openable. A close followed by
the final dispose closes the gateway session once.
Refs #735
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty