Document remote Agent Host connection diagnostics

Product change

• Sources: https://github.com/microsoft/vscode/pull/336214 and https://github.com/microsoft/vscode/pull/336487
• Merged: 2026-09-15T07:04:52Z and 2026-09-17T07:27:46Z

The Agents UI can show a connection diagnostics report for remote hosts, including discovery results, host state, recent activity, and client information. Users can copy, download, refresh, or close the report. The web client also keeps automatic connection attempts visibly in the Connecting state and exposes connection information from the mobile host picker.

Why the docs need an update

docs/agents/run/remote-agent-sessions.md only documents Online and Offline host states and automatic reconnection. It does not explain the diagnostics workflow, pending connection state, or mobile entry point.

Suggested documentation

• docs/agents/run/remote-agent-sessions.md: Add connection-state troubleshooting and the Show Connection Diagnostics or Connection Information workflows, including what refresh does and does not do.

Acceptance criteria

• Remote-session documentation explains how to open and export connection diagnostics.
• The Connecting state and mobile access are covered.
• The documentation does not imply that refreshing diagnostics reconnects a host.