Just to follow up on this, I did get it working eventually. I had a couple false starts, so I think it’s useful to post this for anyone else trying to do this, and to see if someone suggests something I could do better.
First, to go over my solution:
I adding the following to my Home-manager config:
dconf.settings = {
"org/gnome/settings-daemon/plugins/media-keys" = {
custom-keybindings = [
"/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/"
];
};
};
"org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0" = {
binding = "<Primary><Alt>t";
command = "alacritty";
name = "open-terminal";
};
I should note, that the leading and trailing / in custom-keybindings was critical. Originally I didn’t have them, and without that I got into a state where gnome would crash as soon as I logged in. This wasn’t something that went away by booting a previous generation, and the only way I recovered was logging in as root, and restoring ~/.config/dconf/user from a previous filesystem snapshot, git stashing my config changes and doing a nixos-rebuild
Per this, I also had to add the below to get Home-manager to actually apply my dconf changes.
services.dbus.packages = [ pkgs.gnome3.dconf ];
Other than all that, it was easy… 