Tunnel agent host supervisor hangs after 'Resolved server version' (never reaches management-ready) #11940

Environment

• Windows 11 host, VS Code Remote Tunnel (CLI + server 1.145.0, commit a717861c07586a53d83b80d742cd3f59b20a6273)
• agent-host backend
• CLI launched via code-tunnel tunnel service internal-run (log-on startup entry)

Symptom

The agent host supervisor repeatedly wedges during startup. After a tunnel
restart it logs:

[2026-11-04 18:01:40] info Agent host supervisor logging to C:\Users\...\.vscode-server\cli\agent-host-stable.log
[2026-11-04 18:01:41] debug Resolved quality Stable to a717861c07586a53d83b80d742cd3f59b20a6273
[2026-11-04 18:01:41] debug Resolved server version: 1.145.0 (commit a717861c07586a53d83b80d742cd3f59b20a6273)

...and then nothing. It never reaches:

Listening for agent host management requests

Consequences:

• Running servers then log [AgentHostChannel] Upstream connection failed Error: connect ECONNREFUSED 127.0.0.1:<port> every ~30s.
• New chat sessions hang on "Refreshing chat" and the session-target picker
  cannot be changed.
• The wedge recurs roughly every 10-15 minutes after each tunnel restart,
  with occasional healthy windows of 30+ minutes. Occasionally the tunnel's
  relay session also drops ("disconnected primary session after EOF" /
  zombie with no established :443) with zero local network events.

Workaround

Kill all code-tunnel processes (tunnel service + any agent host
processes), then restart the tunnel service. This produces a healthy agent
host that reaches "Server ready", but it wedges again within minutes-to-half
an hour, so it is not a fix - just a reset.

Notes

• Host is fully reachable during the wedge; the tunnel itself stays
  connected (the relay socket is up). Only the agent host hangs.
• A local watchdog now detects this (agent-host process presence + the log
  signature) and restarts the tunnel automatically, capping loops at 4
  restarts/hour. That keeps the box usable but the underlying wedge remains.
• Related: New chats remain stuck in Agent Host after switching back to Local Chat due to persisted chat.userSelectedSessionType vscode#332129 (new chats stuck when
  chat.userSelectedSessionType persists as agent-host) may share a root
  with the session-picker symptom above.