Launch shortcut looks for an installed browser when the configured one is gone
When the configured browser is gone, a change merged into quattro keeps Super + Shift + Return from passing an empty command. A named browser counts only if it is installed, then the lookup falls back to the first installed x-scheme-handler/https handler.
A leftover browser entry after switching browsers left that shortcut with an empty command. When mimeapps.list names that missing browser, xdg-settings and xdg-mime both answer omarchy-browser.desktop. Discarding that answer left omarchy-cmd-default-browser with nothing to print, so omarchy-launch-browser passed uwsm-app an empty command and the shortcut ended in a critical notification that the command was not found.
omarchy-cmd-default-browser accepts an xdg-settings or xdg-mime answer only after installed() agrees. It asks xdg-mime when xdg-settings names a browser that is gone, and falls back to the first installed x-scheme-handler/https handler in mimeinfo.cache. That covers any installed browser, including Helium, Vivaldi and LibreWolf. omarchy-launch-browser reads the Exec line from the same data directories the resolver searched, including the Nix profile, and rejects an empty command before the handoff. omarchy-launch-webapp says web apps need a Chromium-based browser and how to install Chromium, rather than claiming no default browser is set when the default is Firefox.