After removingwsconncache, current versions of Coder will no longer dial agents by the legacy IP address over tailnet. However, backlevel CLIs or Workspace Proxies might, so we keep the IP address around and assign it to agents to they are reachable.

Keeping the address presents no problem now, but we should still eventually remove it since if we ever implement agent-agent networking, or have agents contact clients over tailnet it could cause problems.