The chunked welcome path cleared its snapshot progress timer before
writing the replica file and switching sessions. If that apply work
failed, the frame-apply catch only logged the error, leaving the
initial join promise pending with no welcome/progress timer left to
settle it.
Reject the pending initial join when a welcome or snapshot-chunk apply
fails before the join has completed, preserving reconnect-time logging
for already-joined guests. Add a regression test that forces the replica
write to fail and asserts /join rejects instead of hanging.
Fixes#3144
roboomp
10e1ff44c9