Session.Close now closing its own accepted conn (from the prior fix wave)
made net.ErrClosed on the guacd-side reader indistinguishable from a real
remote failure, so a normal browser-tab close could race the handler's
defer and intermittently log console.proxy_failed on a healthy session.
Add a closing flag, set before Close's sync.Once body actually tears
anything down, that setReason respects -- a deliberate local teardown can
no longer produce or race in a failure reason, while Close's own explicit
reason argument still wins normally.
mrhid6
978b665aa6