programs: prefer the gsettings backend over dconf backend

it's more easily human editable, and programs can write new settings without requiring dbus access

hosts/common/programs/assorted.nix

@@ -279,7 +279,7 @@ in
       "alacritty"  # terminal emulator
       "calls"  # gnome calls (dialer/handler)
       "dbus"
-      "dconf"  # required by many packages, but not well-documented :(
+      "dconf"  # required by many packages, but not well-documented. TODO: REMOVE (use gsettings instead)
       # "delfin"  # Jellyfin client
       "dialect"  # language translation
       "dino"  # XMPP client
@@ -305,6 +305,7 @@ in
       "gnome-screenshot"  # libcamera-based screenshotter, for debugging; should be compatible with gc2145 camera on Pinephone
       "gnome-weather"
       "gpodder"
+      "gsettings"
       "gst-device-monitor"  # for debugging audio/video
       "gst-launch"  # for debugging audio/video
       # "gthumb"

hosts/common/programs/default.nix

@@ -82,6 +82,7 @@
     ./gpsd.nix
     ./gps-share.nix
     ./grimshot.nix
+    ./gsettings.nix
     ./gst-device-monitor.nix
     ./gst-launch.nix
     ./gthumb.nix

hosts/common/programs/gsettings.nix

@@ -0,0 +1,28 @@
+{ config, lib, pkgs, ... }:
+let
+  # [ ProgramConfig ]
+  enabledPrograms = builtins.filter
+    (p: p.enabled && p.gsettings != {})
+    (builtins.attrValues config.sane.programs);
+
+  keyfileTexts = lib.map (p: lib.generators.toDconfINI p.gsettings) enabledPrograms;
+
+  cfg = config.sane.programs.gsettings;
+in
+{
+  sane.programs.gsettings = {
+    packageUnwrapped = pkgs.linkBinIntoOwnPackage pkgs.glib "gsettings";
+    env.GSETTINGS_BACKEND = "keyfile";
+  };
+
+  environment.etc."glib-2.0/settings/defaults" = lib.mkIf cfg.enabled {
+    # GKeyfileSettingsBackend slurps from just two files:
+    # - /etc/glib-2.0/settings/default  (immutable)
+    # - ~/.config/glib-2.0/settings/keyfile  (mutable, and overrides the above)
+    # it doesn't mind me just concatenating everything together though; it handles duplicate groups gracefully.
+    #
+    # for tighter control, /etc/glib-2.0/settings/locks can be used to restrict which values a glib program may write to ~/.config/glib-2.0/settings/keyfile,
+    # but this isn't so much needed for as long as i'm not persisting that keyfile
+    text = lib.mkMerge keyfileTexts;
+  };
+}