dbus: manage it ourselves instead of having systemd do it

hosts/common/polyunfill.nix

@@ -60,6 +60,8 @@ in
         "useradd"
         "userdel"
         "usermod"
+        # from <repo:nixos/nixpkgs:nixos/modules/system/boot/systemd/user.nix>
+        "systemd-user"  #< N.B.: this causes the `systemd --user` service manager to not be started!
       ])) services;
     in lib.mapAttrs (_serviceName: service: service // {
       # replace references with the old pam_unix, which calls into /run/wrappers/bin/unix_chkpwd,

hosts/common/programs/assorted.nix

@@ -254,6 +254,7 @@ in
       # "abaddon"  # discord client
       "alacritty"  # terminal emulator
       "calls"  # gnome calls (dialer/handler)
+      "dbus"
       "dconf"  # required by many packages, but not well-documented :(
       # "delfin"  # Jellyfin client
       "dialect"  # language translation

hosts/common/programs/dbus.nix

@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+let
+  cfg = config.sane.programs.dissent;
+in
+{
+  sane.programs.dbus = {
+    configOption = with lib; mkOption {
+      default = {};
+      type = types.submodule {
+        options.autostart = mkOption {
+          type = types.bool;
+          default = true;
+        };
+      };
+    };
+
+    # normally systemd would create a dbus session for us, but if you configure it not to do that
+    # then we can create our own. not sure if there's a dependency ordering issue here: lots
+    # of things depend on dbus but i don't do anything special to guarantee this is initialized
+    # before them.
+    services.dbus = {
+      description = "dbus user session";
+      partOf = lib.mkIf cfg.config.autostart [ "default" ];
+      command = "dbus-daemon --session --nofork --address=unix:path=/run/user/$UID/bus";
+    };
+  };
+}

hosts/common/programs/default.nix

@@ -24,6 +24,7 @@
     ./cozy.nix
     ./cups.nix
     ./curlftpfs.nix
+    ./dbus.nix
     ./dconf.nix
     ./deadd-notification-center
     ./dialect.nix