Install a desktop update when agents are done, not in the middle of their work

[Dwite]

The problem

When a desktop update is ready, I can only install it now. Installing restarts the app and interrupts agents that are still working. So I keep checking my threads until all of them are finished, and then update by hand.

Continue threads after restarts helps after the restart, but it does not remove the interruption. It is off by default, terminal commands can still be cut off, and some threads need a new message to continue.

What I would like

A second choice next to Update now: Update when idle.

• The app waits until no agent is working, then installs the update.
• "Working" means a turn is starting or running, an agent waits for approval or for my answer, or a background agent is active.
• A notice stays on screen while the update waits. It has a Cancel button.
• If a newer version downloads while it waits, the schedule is cancelled.

Limits

• Desktop app only. Updates for remote servers and for the mobile app stay as they are.
• The window must stay open. Closing or reloading it clears the schedule.
• Terminal commands do not count as work.
• The check runs in the app, not on the server. It cannot stop a new turn that starts at the same moment as the install.

What I am asking

• Do you want this behavior?
• Is the scope right? A smaller option is to only show which agents are still working before I confirm the update.

I built a version before asking, which was my mistake. It is closed, but it has screenshots and a short demo: #12607.