The wrapGL wrapper had #!/bin/bash which doesn't exist on NixOS, so niri's execvp("ghostty") was failing silently. Shells masked the bug by falling back through sh. Switch to ${pkgs.runtimeShell}. Also fix useNixGL: the check '"system" ? config' always returned false (tested attribute on a string, not an attrset), causing ghostty to be nixGL-wrapped on NixOS where native Mesa works. Use osConfig == null to detect standalone home-manager instead.