test: remote agent host connection diagnostics

Refs: #336443, #336487

• web
• web (mobile)

Complexity: 3

Authors: @amunger

Verify that remote Agent Host connection state and diagnostic evidence are actionable and accurate in the web Agents Window, including its mobile layout.

Feel free to create issues around connectivity problems that come up during testing, but this is mostly about enabling us to troubleshoot those issues through the collected diagnostics, especially on mobile, where logs are much more difficult to see.

Set up

1. Make sure you have at least one remote agent host enabled
   a. with CLI: code-insiders agent --tunnel
   b. in agents window: click the "allow connections..." button in the top right

Testing

1. Open insiders.vscode.dev/agents (or even better, download/open the PWA on mobile)
2. click the info icon to see the diagnostic view of the remote connections (within the host list on mobile)

3. try to transfer that information into a chat session and see if the agent has context to diagnose questions you have

e.g. "why is ... not connected?", "how long does it take to connect to my dev tunnel?"

Use a build containing #336443 and #336487, open the web Agents Window at /agents, and enable chat.remoteAgentHostsEnabled. Verify that remote Agent Host connection state and diagnostic evidence are understandable and accurate in the web layout and in mobile or phone emulation; completion means both checks pass.