dbus: Switch default implementation to broker

nixos/doc/manual/release-notes/rl-2405.section.md

@@ -40,6 +40,8 @@ Use `services.pipewire.extraConfig` or `services.pipewire.configPackages` for Pi
 - A new option `systemd.sysusers.enable` was added. If enabled, users and
   groups are created with systemd-sysusers instead of with a custom perl script.
 
+- The default dbus implementation has transitioned to dbus-broker from the classic dbus daemon for better performance and reliability. Users can revert to the classic dbus daemon by setting `services.dbus.implementation = "dbus";`. For detailed deviations, refer to [dbus-broker's deviations page](https://github.com/bus1/dbus-broker/wiki/Deviations).
+
 - A new option `virtualisation.containers.cdi` was added. It contains `static` and `dynamic` attributes (corresponding to `/etc/cdi` and `/run/cdi` respectively) to configure the Container Device Interface (CDI).
 
 - `virtualisation.docker.enableNvidia` and `virtualisation.podman.enableNvidia` options are deprecated. `virtualisation.containers.cdi.dynamic.nvidia.enable` should be used instead. This option will expose GPUs on containers with the `--device` CLI option. This is supported by Docker 25, Podman 3.2.0 and Singularity 4. Any container runtime that supports the CDI specification will take advantage of this feature.

nixos/modules/services/system/dbus.nix

@@ -39,7 +39,7 @@ in
 
       implementation = mkOption {
         type = types.enum [ "dbus" "broker" ];
-        default = "dbus";
+        default = "broker";
         description = lib.mdDoc ''
           The implementation to use for the message bus defined by the D-Bus specification.
           Can be either the classic dbus daemon or dbus-broker, which aims to provide high