Host: `updater::check_now` runs the same check the timer runs (the same updater endpoint, nothing else) for the app's shell-only `update_check`. It never queues or retries: while a check is in flight (the timer's or an earlier request's), or within 10 seconds of the last request, it only answers with the current status (`update::may_check_now`, tested). The timer's loop uses the same single-flight guard.
Frame: the menu's Updates row is that check (`updateRow`, tested): "Checking…", "Up to date · <version>", "Downloading <version>…", "Restart to update" when an update is ready (the row then installs it), and "Could not check" with a plain sentence as its tooltip when the server does not answer. The updater's error text is never shown there, and a failure is only mentioned when the owner asked for the check in this menu; the timer's own failures stay quiet.