Write final static netplan during install

autoinstall/user-data

@@ -7,40 +7,23 @@ autoinstall:
   keyboard:
     layout: us
 
-  # ── Network: apply known-good static defaults ─
-  # We no longer pause on the installer network screen because Subiquity was
-  # accepting the IP but dropping the default gateway on console installs.
-  # Bring the VM up directly on the standard Cezen static network instead.
+  # ── Network: keep installer boot simple; write final netplan ourselves ─
+  # Subiquity was repeatedly bringing the target system up without the default
+  # route, even when the static gateway was supplied. Use DHCP only for the
+  # installer environment, then write the final static netplan file directly
+  # into the installed system in late-commands.
   network:
     network:
       version: 2
       ethernets:
         any-en:
-          dhcp4: false
+          dhcp4: true
           match:
             name: "en*"
-          addresses:
-            - 172.16.10.181/23
-          routes:
-            - to: default
-              via: 172.16.10.1
-          nameservers:
-            addresses:
-              - 8.8.8.8
-              - 1.1.1.1
         any-eth:
-          dhcp4: false
+          dhcp4: true
           match:
             name: "eth*"
-          addresses:
-            - 172.16.10.181/23
-          routes:
-            - to: default
-              via: 172.16.10.1
-          nameservers:
-            addresses:
-              - 8.8.8.8
-              - 1.1.1.1
 
   # ── Storage: LVM using ALL disk space ─────────
   storage:
@@ -80,6 +63,27 @@ autoinstall:
     - echo "cezen ALL=(ALL) NOPASSWD:ALL" > /target/etc/sudoers.d/cezen
     - chmod 440 /target/etc/sudoers.d/cezen
 
+    # Replace the installer-generated network config with the final static
+    # Cezen network so the installed system always has the expected route.
+    - rm -f /target/etc/netplan/50-cloud-init.yaml /target/etc/netplan/00-installer-config.yaml || true
+    - |
+      cat > /target/etc/netplan/99-cezen-static.yaml << 'EOF'
+      network:
+        version: 2
+        ethernets:
+          ens18:
+            dhcp4: false
+            addresses:
+              - 172.16.10.181/23
+            routes:
+              - to: default
+                via: 172.16.10.1
+            nameservers:
+              addresses:
+                - 8.8.8.8
+                - 1.1.1.1
+      EOF
+
     # Disable the installer media APT source so post-install apt uses network
     # mirrors instead of the custom ISO content.
     - sed -i 's/^deb cdrom:/# deb cdrom:/' /target/etc/apt/sources.list || true