fix(wallpaper): repaint monitors hotplugged after login

awww-daemon paints only the outputs present when `awww img` last ran and does
not repaint a monitor connected later, so it comes up on the daemon's black
fill — which a transparent foot then shows instead of the wallpaper. Add
`wallpaper-hotplug`: it watches Hyprland's event socket and re-runs `setbg`
(which pushes to all outputs) on each `monitoradded`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home.nix

@@ -614,6 +614,8 @@ in
         # the ~/.local/share/bg symlink if it exists.
         "awww-daemon"
         "sh -c '[ -e \"$HOME/.local/share/bg\" ] && awww img \"$HOME/.local/share/bg\"'"
+        # re-push the wallpaper onto monitors connected after login (media.nix)
+        "wallpaper-hotplug"
       ];
     };
   };

modules/media.nix

@@ -17,6 +17,22 @@ let
     [ -n "$1" ] && ln -sf "$(readlink -f "$1")" "$bgloc"
     ${pkgs.awww}/bin/awww img "$bgloc"
   '';
+
+  # awww-daemon paints only the outputs present when `awww img` last ran and does
+  # not repaint a monitor hotplugged afterwards — it comes up on the fill color
+  # (black), and a transparent foot on it then shows that black, not the
+  # wallpaper. Watch Hyprland's event socket and re-push the wallpaper (setbg
+  # with no arg → all current outputs) on each monitor-add. Hyprland emits both
+  # `monitoradded` and `monitoraddedv2`; match only the former so setbg fires
+  # once. Runs as a Hyprland exec-once (see home.nix).
+  wallpaperHotplug = pkgs.writeShellScriptBin "wallpaper-hotplug" ''
+    sock="''${XDG_RUNTIME_DIR}/hypr/''${HYPRLAND_INSTANCE_SIGNATURE}/.socket2.sock"
+    ${pkgs.socat}/bin/socat -u UNIX-CONNECT:"$sock" - | while IFS= read -r line; do
+      case "$line" in
+        "monitoradded>>"*) setbg ;;
+      esac
+    done
+  '';
 in
 {
   programs.mpv = {
@@ -50,6 +66,7 @@ in
 
   home.packages = with pkgs; [
     setbg
+    wallpaperHotplug # re-push wallpaper to a hotplugged monitor (see comment above)
     awww            # wayland wallpaper daemon (setbg backend)
     wl-clipboard    # wl-copy, for the yank binds
     imagemagick     # `magick`: rotate/flip binds