Desktop remote thread index can stall when an unrelated remote environment is offline

Summary

In the desktop app, an unavailable remote environment can prevent the global thread/history index from loading. Tasks on other, healthy remote environments continue to start and run, but their conversations and progress do not become visible in the desktop UI.

Steps to reproduce

1. Configure multiple remote environments in the desktop app.
2. Leave one remote environment unavailable.
3. Start a project task on a different, reachable remote environment.
4. Open the all-host thread/history view or wait for the task to report progress.

Actual behavior

• The global thread/history request does not complete.
• The app records an offline remote-connection failure.
• The renderer subsequently receives turn events for conversations it has not registered.
• The task runs on the reachable environment, but its thread and progress are not visible or monitorable in the desktop UI.

Expected behavior

An unavailable remote environment should be isolated from unrelated remote environments. The desktop app should still list, open, and monitor tasks running on reachable environments, and should retain task events until the corresponding conversation is registered.

Additional context

This appears related to #35666, but is distinct: the task is not merely losing a progress bar; the cross-environment thread registry appears blocked by one offline connection. The interactive CLI and the app-server worker can also report different bundled runtime versions, which may be relevant to diagnosis.

No host names, account details, task contents, conversation identifiers, or logs are included in this report.

Start by tracing the desktop app's global thread/history loading, remote-connection failure handling, and conversation event registration. Reproduce the case with one unavailable and one reachable remote environment, then verify that reachable tasks remain visible and their events are retained until the conversation is registered.