fix: keep systemd-resolved enabled on both hosts

README.md

@@ -129,6 +129,12 @@ includes **Playwright CLI + matching Firefox**, with a writable, once-seeded
 Web profile on first startup, retained on restarts and updated explicitly. No host
 service is activated.
 
+### System DNS
+
+`network.nix` enables **`systemd-resolved.service` on both hosts at boot**, with automatic restart after five seconds and no retry limit. NetworkManager supplies per-link DNS on the laptop; EC2 retains dhcpcd. NixOS connects `/etc/resolv.conf` to resolved's stub and provides the D-Bus service used by `resolvectl`. Upstream DNS still comes from DHCP/VPN configuration, not hard-coded public or private servers. An explicit `systemctl stop systemd-resolved` still stops it normally.
+
+Use `systemctl status systemd-resolved` and `resolvectl status` to inspect it. `sudo resolvectl dns krishna-laptop 192.168.1.19` sets DNS on that existing interface at runtime; it does not persist across interface recreation or reboot. Put persistent VPN DNS and any routing domains in the VPN/NetworkManager profile.
+
 ### Local Tor client
 
 On both hosts, `network.nix` installs Tor from the **system pin** and enables `tor.service` at boot. It runs as the dedicated `tor` user with the NixOS module's sandbox and private persistent state in `/var/lib/tor`. Systemd restarts an exited daemon after five seconds without a retry limit; an explicit `systemctl stop tor` still stops it normally. A running process does not guarantee network connectivity—check for `Bootstrapped 100%` in the journal.

network.nix

@@ -1,5 +1,4 @@
 {
-  config,
   inputs,
   lib,
   pkgs,
@@ -8,14 +7,14 @@
 let
   latest = import inputs.nixpkgs-latest {
     inherit (pkgs.stdenv.hostPlatform) system;
-    config = pkgs.config;
+    inherit (pkgs) config;
   };
 in
 {
-  # NetworkManager owns local DNS on workstations. With dhcpcd (EC2),
-  # NixOS wires resolvconf to resolved. Preserve both hosts' existing behavior.
+  # Keep resolvectl available on both hosts. NixOS wires NetworkManager and
+  # /etc/resolv.conf to resolved; DHCP/VPNs still supply the upstream DNS.
   services.resolved = {
-    enable = lib.mkDefault (!config.networking.networkmanager.enable);
+    enable = true;
     settings.Resolve = {
       LLMNR = false;
       MulticastDNS = false;
@@ -23,6 +22,15 @@ in
     };
   };
 
+  # The NixOS module enables resolved at boot. Retry exits without a start limit.
+  systemd.services.systemd-resolved = {
+    unitConfig.StartLimitIntervalSec = 0;
+    serviceConfig = {
+      Restart = "always";
+      RestartSec = "5s";
+    };
+  };
+
   # Local, opt-in SOCKS client only. Keep the daemon on the system package pin.
   # No relay/exit, control listener, transparent proxy or host DNS changes.
   services.tor = {

physical-test.nix

@@ -84,11 +84,38 @@ let
     {
       assertion =
         config.networking.networkmanager.enable
-        && !config.services.resolved.enable
+        && config.networking.networkmanager.dns == "systemd-resolved"
         && builtins.elem (lib.getName pkgs.networkmanager-openvpn) (
           map lib.getName config.networking.networkmanager.plugins
         );
-      message = "Keep NetworkManager/DNS and provide its OpenVPN integration.";
+      message = "Keep NetworkManager with resolved DNS and its OpenVPN integration.";
+    }
+    {
+      assertion =
+        lib.all
+          (
+            c:
+            let
+              unit = c.systemd.services.systemd-resolved;
+            in
+            c.services.resolved.enable
+            && builtins.elem "sysinit.target" unit.wantedBy
+            && builtins.elem "dbus-org.freedesktop.resolve1.service" unit.aliases
+            && unit.serviceConfig.Restart == "always"
+            && unit.serviceConfig.RestartSec == "5s"
+            && unit.unitConfig.StartLimitIntervalSec == 0
+            && !c.networking.resolvconf.enable
+            && c.networking.resolvconf.package == c.systemd.package
+            && c.environment.etc."resolv.conf".source == "/run/systemd/resolve/stub-resolv.conf"
+            && c.services.resolved.settings.Resolve.DNS == [ ]
+            && !c.services.resolved.settings.Resolve.LLMNR
+            && !c.services.resolved.settings.Resolve.MulticastDNS
+          )
+          [
+            config
+            ec2Config
+          ];
+      message = "Both hosts need boot-enabled, restarting resolved with D-Bus/stub DNS integration, without hard-coded DNS servers.";
     }
     {
       assertion =
@@ -232,7 +259,7 @@ pkgs.runCommand "physical-config-check" { } ''
   test -f "$sessions/wayland-sessions/hyprland-uwsm.desktop"
   test ! -e "$sessions/wayland-sessions/hyprland.desktop"
   for tool in wg wg-quick openvpn iperf3 nmap traceroute whois mtr dig tcpdump ethtool nc socat \
-    fping drill torsocks proxychains4 tor nm-connection-editor; do
+    fping drill torsocks proxychains4 tor nm-connection-editor resolvectl; do
     test -x "${config.system.path}/bin/$tool"
   done
   # Validate the exact generated torrc offline without touching live Tor state.