Move KDE desktop to host; container becomes noVNC proxy only

The vnc-desktop container no longer runs a desktop environment. KDE Plasma
and Xvnc now run directly on the host via a vnc-kde systemd service, with
port 5901 firewalled to the podman bridge subnet only. The container is
reduced to a websockify bridge forwarding the noVNC web UI to hetzner-host:5901.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nixos/firewall.nix

@@ -20,5 +20,6 @@
   networking.firewall.extraCommands = ''
     iptables -I nixos-fw -s 10.89.0.0/16 -p udp --dport 53 -j nixos-fw-accept
     iptables -I nixos-fw -s 10.89.0.0/16 -p tcp --dport 53 -j nixos-fw-accept
+    iptables -I nixos-fw -s 10.89.0.0/16 -p tcp --dport 5901 -j nixos-fw-accept
   '';
 }

nixos/linux.nix

@@ -102,6 +102,61 @@ in {
     }
   ];
 
+  # KDE Plasma on the host — the noVNC container (vnc-desktop) is a thin WebSocket
+  # proxy that connects to the VNC server started here.
+  services.xserver = {
+    enable = true;
+    desktopManager.plasma5.enable = true;
+  };
+  # Don't start X via a display manager; the vnc-kde service owns the session.
+  services.displayManager.sddm.enable = lib.mkForce false;
+
+  systemd.services.vnc-kde = {
+    description = "KDE Plasma desktop accessible over VNC";
+    wantedBy = [ "multi-user.target" ];
+    after = [ "network.target" "agenix.service" ];
+
+    path = with pkgs; [
+      tigervnc
+      dbus
+      xorg.xauth
+      plasma5Packages.plasma-workspace
+      coreutils
+      gnugrep
+    ];
+
+    serviceConfig = {
+      Type = "simple";
+      User = "root";
+      Restart = "on-failure";
+      RestartSec = "5s";
+      TasksMax = "infinity";
+
+      ExecStart = pkgs.writeShellScript "vnc-kde-start" ''
+        set -e
+        rm -f /tmp/.X1-lock /tmp/.X11-unix/X1
+
+        mkdir -p /root/.vnc
+        VNC_PASSWORD=$(grep '^VNC_PASSWORD=' /run/agenix/vnc-password | cut -d= -f2-)
+        printf '%s' "$VNC_PASSWORD" | vncpasswd -f > /root/.vnc/passwd
+        chmod 600 /root/.vnc/passwd
+
+        Xvnc :1 \
+            -rfbport 5901 \
+            -SecurityTypes VncAuth \
+            -PasswordFile /root/.vnc/passwd \
+            -geometry 1920x1080 \
+            -depth 24 \
+            -AlwaysShared &
+
+        export DISPLAY=:1
+        sleep 2
+
+        exec dbus-run-session -- startplasma-x11
+      '';
+    };
+  };
+
   virtualisation.arion = {
     backend = "podman-socket";
     projects.forgejo.settings = import ./arion/arion-compose.nix;

nixos/vnc-desktop/Dockerfile

@@ -3,25 +3,10 @@ FROM ubuntu:24.04
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && apt-get install -y \
-    tigervnc-standalone-server \
-    tigervnc-common \
     novnc \
     python3-websockify \
-    kde-plasma-desktop \
-    konsole \
-    x11-utils \
-    xfonts-base \
-    dbus-x11 \
-    openssh-client \
-    curl \
     && rm -rf /var/lib/apt/lists/*
 
-# Remove Bluetooth stack — obexd gets activated in a tight loop by kded5
-# inside the container (no BT hardware), which exhausts the process limit.
-RUN apt-get purge -y --auto-remove bluez bluez-obexd 2>/dev/null || true; \
-    rm -f /usr/share/dbus-1/services/org.bluez.obex.service \
-          /usr/share/dbus-1/system-services/org.bluez.service
-
 COPY start.sh /start.sh
 RUN chmod +x /start.sh
 

nixos/vnc-desktop/start.sh

@@ -1,31 +1,5 @@
 #!/bin/bash
 set -e
 
-mkdir -p /root/.vnc /root/.ssh
+# Proxy WebSocket (6080) → VNC server running on the host (hetzner-host:5901)
-chmod 700 /root/.ssh
+exec websockify --web /usr/share/novnc 6080 hetzner-host:5901
-
-# Clean up stale X lock files from previous container runs
-rm -f /tmp/.X1-lock /tmp/.X11-unix/X1
-
-# Set VNC password from environment
-echo "${VNC_PASSWORD:?VNC_PASSWORD must be set}" | vncpasswd -f > /root/.vnc/passwd
-chmod 600 /root/.vnc/passwd
-
-# Start Xvnc (headless X server + VNC server in one)
-Xvnc :1 \
-    -rfbport 5901 \
-    -SecurityTypes VncAuth \
-    -PasswordFile /root/.vnc/passwd \
-    -geometry 1920x1080 \
-    -depth 24 \
-    -AlwaysShared \
-    &
-
-export DISPLAY=:1
-sleep 2
-
-# Start KDE Plasma session
-dbus-run-session -- startplasma-x11 &
-
-# Serve noVNC web UI + bridge WebSocket -> VNC
-exec websockify --web /usr/share/novnc 6080 localhost:5901