manatee: Ensure local traffic works next to VPN

hosts/manatee/modules/network/default.nix

@@ -1,4 +1,7 @@
 { ... }:
+let
+  hostAddress = "192.168.50.203";
+in
 {
   networking = {
     hostName = "manatee";
@@ -15,7 +18,7 @@
         ipv4 = {
           addresses = [
             {
-              address = "192.168.50.203";
+              address = hostAddress;
               prefixLength = 24;
             }
           ];
@@ -34,11 +37,14 @@
       };
     };
 
-    # Route packets from machines local IP back to router
     localCommands = ''
-      # Add the rule only if it doesn't exist yet (idempotent)
-      ip rule list | grep -q "from 192.168.50.203 lookup 100" || \
-      ip rule add from 192.168.50.203 lookup 100 priority 5000
+      # Ensure local LAN traffic uses the main table, e.g. responds to the local machine
+      ip rule list | grep -q "192.168.50.0/24 lookup main" || \
+      ip rule add to 192.168.50.0/24 lookup main priority 4999
+
+      # All other traffic from this IP uses Table 100 (e.g. responds to router and back out)
+      ip rule list | grep -q "from ${hostAddress} lookup 100" || \
+      ip rule add from ${hostAddress} lookup 100 priority 5000
     '';
   };
 }