feat(beszel): add beszel agent to tailscale-router

Wires beszel-agent into all tailscale-router variants (lxc/linode/proxmox)
by importing enable-agent.nix in the build type and host-token.nix in the
host file. Adds the sops creation rule for secrets/tailscale-router.yaml
(all three platform variants as recipients). The secrets file must be
created manually before deploying — see instructions in PR.

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

.sops.yaml

@@ -77,6 +77,14 @@ creation_rules:
           - *admin
           - *lxc-tor-relay
 
+  - path_regex: secrets/tailscale-router\.yaml$
+    key_groups:
+      - age:
+          - *admin
+          - *linode-tailscale-router
+          - *lxc-tailscale-router
+          - *proxmox-tailscale-router
+
   # gui-host-specific secrets (currently: wifi-password, see
   # modules/networking/wifi.nix). Only *lxc-gui has a registered key today
   # -- proxmox-gui/linode-gui/baremetal-gui haven't been provisioned via

hosts/tailscale-router/host.nix

@@ -1,8 +1,19 @@
 _:
 
 {
+  imports = [
+    (import ../../modules/beszel/host-token.nix {
+      name = "tailscale-router";
+      sopsFile = ../../secrets/tailscale-router.yaml;
+    })
+  ];
+
   networking.hostName = "tailscale-router";
 
+  services.beszel.agent.environment = {
+    KEY = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFPR9kwtC4TAeTRu46A7+opZsYpxqkRJ+x/ZyB2GWCeG";
+  };
+
   # No networking.hostId: only ZFS-touching hosts (server, docker) need one
   # for pool-import safety, and this host does neither.
 

modules/build-types/tailscale-router.nix

@@ -3,6 +3,7 @@
 {
   imports = [
     ../tailscale/subnet-router.nix
+    ../beszel/enable-agent.nix
   ];
 
   # "server", not "both": this build type advertises LAN subnet routes but
@@ -16,27 +17,29 @@
   # Must also be approved in the Tailscale admin console (Machines → Edit route settings).
   services.tailscale.extraUpFlags = [ "--advertise-routes=${vars.lanCidr}" ];
 
-  networking.firewall = {
+  networking = {
+    # SNAT traffic from LAN machines going out through Tailscale so the remote
+    # peer sees it sourced from this router's Tailscale IP (100.x.x.x) rather
+    # than a raw LAN IP.  Without this, Tailscale drops the forwarded packets
+    # because the source is not a recognised Tailscale address.
+    #
+    # networking.nat.externalInterface alone does not insert a MASQUERADE rule
+    # (it only does so when internalInterfaces is also set).  We use
+    # extraCommands to add the rule into the nixos-nat-post chain that
+    # networking.nat.enable creates, and extraStopCommands to clean it up.
+    nat.enable = true;
+
+    firewall = {
       # Forwarded subnet-router traffic arrives on tailscale0 already
       # tailscale-authenticated -- the firewall's normal per-port allow-list
       # would otherwise drop it. Standard NixOS/Tailscale subnet-router guidance.
       trustedInterfaces = [ "tailscale0" ];
-
-    # SNAT LAN traffic going into Tailscale so the remote peer sees it as
-    # coming from this router's Tailscale IP rather than a raw LAN IP.
-    # Without this, Tailscale drops forwarded packets whose source is not a
-    # recognised Tailscale address.
-    #
-    # We target POSTROUTING directly (always-existing built-in chain) rather
-    # than nixos-nat-post: extraCommands runs after the old nixos-nat-post is
-    # deleted but before the new one is created, so -A nixos-nat-post silently
-    # fails.  The -C check makes the rule idempotent across firewall reloads.
       extraCommands = ''
-      iptables -t nat -C POSTROUTING -s ${vars.lanCidr} -o tailscale0 -j MASQUERADE 2>/dev/null || \
-        iptables -t nat -A POSTROUTING -s ${vars.lanCidr} -o tailscale0 -j MASQUERADE
+        iptables -t nat -A nixos-nat-post -s ${vars.lanCidr} -o tailscale0 -j MASQUERADE
       '';
       extraStopCommands = ''
-      iptables -t nat -D POSTROUTING -s ${vars.lanCidr} -o tailscale0 -j MASQUERADE 2>/dev/null || true
+        iptables -t nat -D nixos-nat-post -s ${vars.lanCidr} -o tailscale0 -j MASQUERADE 2>/dev/null || true
       '';
     };
+  };
 }