Privacy-filtered excerpts of actual desktop/sshd output (paths, tokens, and unrelated startup output omitted).

Fixture authentication:
Accepted keyboard-interactive/pam for proofuser from 127.0.0.1 port 34578 ssh2

Base:
[23:45:37.012] ssh.remoteServer.launch.start
Tunnel command included: ControlMaster=no, ControlPath=none, ControlPersist=no
stderr: proofuser@127.0.0.1: Permission denied (keyboard-interactive).
[23:45:41.097] ssh.auth.passwordPrompt.request, attempt: 1
[23:46:13.013] ssh.auth.passwordPrompt.request, attempt: 2
Final UI: Could not prepare the SSH environment: Error invoking remote method 'desktop:ensure-ssh-environment': SshCommandError: proofuser@127.0.0.1: Permission denied (keyboard-interactive).

Head:
[23:46:21.582] ssh.tunnel.process.exited (initial independent login denied)
[23:46:21.608] ssh.tunnel.ready.failed
[23:46:21.773] ssh.tunnel.ready
[23:46:22.228] ssh.environment.ensure.succeeded
  localPort: 39363, remotePort: 3774, remoteServerKind: managed, issuedPairingToken: true
[23:48:48.812] ssh.tunnel.close.succeeded

Actual socket probes:
Before disconnect: OPEN
After Settings > Environments > Switch off: ECONNREFUSED
ssh -O check proof-otp: Master running (pid=57949)