feat: add sd flash command and rekey ages

flake.nix

@@ -98,10 +98,88 @@
           cargoArtifacts = piArtifacts;
         }
       );
+
+      flash-pi-sd = pkgs.writeShellApplication {
+        name = "flash-pi-sd";
+        runtimeInputs = [
+          agenix.packages.${system}.default
+          pkgs.coreutils
+          pkgs.nix
+          pkgs.systemd
+          pkgs.util-linux
+          pkgs.zstd
+        ];
+        text = ''
+          set -euo pipefail
+
+          if [ "$#" -ne 1 ]; then
+            echo "usage: flash-pi-sd /dev/sdX" >&2
+            exit 1
+          fi
+
+          device="$1"
+          flake_path=${builtins.toString ./.}
+          image_link="$(mktemp -u /tmp/noisebell-sd-image.XXXXXX)"
+          mount_dir="$(mktemp -d)"
+          key_file="${builtins.toString ./secrets/bootstrap-identity.age}"
+          rules_file="${builtins.toString ./secrets/secrets.nix}"
+
+          cleanup() {
+            if mountpoint -q "$mount_dir"; then
+              sudo umount "$mount_dir"
+            fi
+            rm -rf "$mount_dir"
+            rm -f "$image_link"
+          }
+          trap cleanup EXIT
+
+          if [ ! -b "$device" ]; then
+            echo "not a block device: $device" >&2
+            exit 1
+          fi
+
+          boot_part="''${device}1"
+          case "$device" in
+            *[0-9]) boot_part="''${device}p1" ;;
+          esac
+
+          echo "Building bootstrap SD image..."
+          nix build "$flake_path#nixosConfigurations.bootstrap.config.system.build.sdImage" -o "$image_link"
+
+          image="$(echo "$image_link"/sd-image/*.img*)"
+          if [ ! -f "$image" ]; then
+            echo "failed to locate SD image under $image_link/sd-image" >&2
+            exit 1
+          fi
+
+          echo "Flashing $image to $device..."
+          if [ "''${image##*.}" = "zst" ]; then
+            zstd -d --stdout "$image" | sudo dd of="$device" bs=4M conv=fsync status=progress
+          else
+            sudo dd if="$image" of="$device" bs=4M conv=fsync status=progress
+          fi
+          sync
+
+          sudo partprobe "$device"
+          sudo udevadm settle
+
+          if findmnt -rn "$boot_part" >/dev/null 2>&1; then
+            sudo umount "$boot_part"
+          fi
+
+          echo "Installing bootstrap age identity onto $boot_part..."
+          sudo mount "$boot_part" "$mount_dir"
+          RULES="$rules_file" agenix -d "$key_file" | sudo tee "$mount_dir/noisebell-bootstrap.agekey" >/dev/null
+          sudo chmod 600 "$mount_dir/noisebell-bootstrap.agekey"
+          sync
+
+          echo "Done. You can now move the card to the Pi and boot it."
+        '';
+      };
     in
     {
       packages.${system} = {
-        inherit noisebell-cache noisebell-discord;
+        inherit noisebell-cache noisebell-discord flash-pi-sd;
         default = noisebell-cache;
       };
 
@@ -136,7 +214,14 @@
 
       nixosConfigurations.bootstrap = nixpkgs.lib.nixosSystem {
         system = "aarch64-linux";
-        modules = [ ./pi/bootstrap.nix ];
+        modules = [
+          agenix.nixosModules.default
+          (import ./pi/module.nix {
+            pkg = noisebell-pi;
+            rev = self.shortRev or "dirty";
+          })
+          ./pi/bootstrap.nix
+        ];
       };
 
       devShells.${system}.default = craneLib.devShell {
@@ -145,5 +230,10 @@
           agenix.packages.${system}.default
         ];
       };
+
+      apps.${system}.flash-pi-sd = {
+        type = "app";
+        program = "${flash-pi-sd}/bin/flash-pi-sd";
+      };
     };
 }

pi/README.md

@@ -26,20 +26,25 @@ boot.binfmt.emulatedSystems = [ "aarch64-linux" ];
 
 ### 1. Flash the SD card
 
+Preferred: one command builds the bootstrap image, writes it to the SD card, and installs the
+bootstrap agenix identity onto the boot partition so the full Pi system can come up on first boot:
+
+```sh
+nix run .#flash-pi-sd -- /dev/sdX
+```
+
+This bootstrap image already includes the normal Noisebell service, Tailscale, and the Pi config.
+
+Manual build if you need it:
+
 ```sh
 nix build .#nixosConfigurations.bootstrap.config.system.build.sdImage
 dd if=result/sd-image/*.img of=/dev/sdX bs=4M status=progress
 ```
 
-Boot the Pi. It connects to the Noisebridge WiFi automatically and is discoverable via mDNS as `noisebridge-pi.local`.
+Boot the Pi. It connects to the Noisebridge WiFi automatically.
 
-### 2. Find the Pi
-
-```sh
-ping noisebridge-pi.local
-```
-
-### 3. SSH host key
+### 2. SSH host key
 
 Grab the key and add it to `secrets/secrets.nix`:
 
@@ -59,7 +64,7 @@ in
 }
 ```
 
-### 4. Create secrets
+### 3. Create secrets
 
 ```sh
 cd secrets
@@ -68,6 +73,29 @@ agenix -e inbound-api-key.age    # key the cache uses to poll us
 agenix -e tailscale-auth-key.age # tailscale auth key
 ```
 
+### 4. Bootstrap agenix identity
+
+The Pi uses a dedicated bootstrap age identity stored at `/boot/noisebell-bootstrap.agekey` to
+decrypt its runtime secrets, so first boot does not depend on the machine's freshly generated SSH
+host key.
+
+To refresh recipients after changing `secrets/secrets.nix`:
+
+```sh
+cd secrets
+agenix -r
+```
+
+If you use `nix run .#flash-pi-sd -- /dev/sdX`, this file is installed automatically.
+
+To install the bootstrap identity manually onto a flashed card before first boot:
+
+```sh
+cd secrets
+agenix -d bootstrap-identity.age > /boot/noisebell-bootstrap.agekey
+chmod 600 /boot/noisebell-bootstrap.agekey
+```
+
 ### 5. SSH access
 
 Add your public key to `configuration.nix`:
@@ -80,6 +108,9 @@ users.users.root.openssh.authorizedKeys.keys = [
 
 ### 6. Deploy
 
+After first boot, the Pi should already be running the normal service stack from the flashed image.
+Use this only for later updates:
+
 ```sh
 nixos-rebuild switch --flake .#pi --target-host root@noisebell
 ```

pi/bootstrap.nix

@@ -1,32 +1,8 @@
 { modulesPath, ... }:
 
 {
-  imports = [ "${modulesPath}/installer/sd-card/sd-image-aarch64.nix" ];
-
-  hardware.enableRedistributableFirmware = true;
-
-  networking.hostName = "noisebridge-pi";
-
-  networking.wireless = {
-    enable = true;
-    networks = {
-      "Noisebridge" = {
-        psk = "noisebridge";
-      };
-    };
-  };
-
-  services.avahi = {
-    enable = true;
-    nssmdns4 = true;
-    publish = {
-      enable = true;
-      addresses = true;
-    };
-  };
-
-  services.openssh.enable = true;
-  users.users.root.openssh.authorizedKeys.keys = [
-    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIE40ISu3ydCqfdpb26JYD5cIN0Fu0id/FDS+xjB5zpqu"
+  imports = [
+    "${modulesPath}/installer/sd-card/sd-image-aarch64.nix"
+    ./configuration.nix
   ];
 }

pi/configuration.nix

@@ -1,4 +1,4 @@
-{ config, pkgs, ... }:
+{ config, ... }:
 
 {
   system.stateVersion = "24.11";
@@ -10,16 +10,14 @@
     networks."Noisebridge".psk = "noisebridge";
   };
 
-  services.avahi = {
-    enable = true;
-    nssmdns4 = true;
-    publish = {
-      enable = true;
-      addresses = true;
-    };
-  };
+  services.avahi.enable = false;
 
   # Decrypted at runtime by agenix
+  age.identityPaths = [
+    "/boot/noisebell-bootstrap.agekey"
+    "/etc/ssh/ssh_host_ed25519_key"
+  ];
+
   age.secrets.tailscale-auth-key.file = ../secrets/tailscale-auth-key.age;
   age.secrets.pi-to-cache-key.file = ../secrets/pi-to-cache-key.age;
   age.secrets.cache-to-pi-key.file = ../secrets/cache-to-pi-key.age;
@@ -32,7 +30,10 @@
     inboundApiKeyFile = config.age.secrets.cache-to-pi-key.path;
   };
 
-  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ];
 
   services.tailscale = {
     enable = true;

secrets/discord-token.age

@@ -1,7 +1,8 @@
 age-encryption.org/v1
--> ssh-ed25519 Ziw7aw luObn0XSH0tR4UpGDc2QWUFGSpwVuBuGhmgCWW/IlGs
-hJRSk4yw3EzD0meybEcpJ8CVmnROuriLVmTJAtd+mdM
--> ssh-ed25519 uKftJg t/1U0LiOFgtiMzxELdnv4NZKWR3O8Oj1zQKi1nWWXHg
-BuBBODNVO8bq9yf5idOC7/dUTgsxPd4a56JNcbTQUIQ
---- jhW7YACeM6wl4AUih6GQ9Qx9eaOHkNIS8BYp8vroD7k
-s–lHhu9ûGš¥8<êX†j車{^žÎ„”N o­Þ9êœÆy†ÉŠ}¤ÔBš  ¨
®È}ZëE<C3AB>†aܧ
:Öžð#úÔpÕ8ZÛåyÚNåí3-×NdP³$JÅ€é<E282AC>
PìÛ\
+-> ssh-ed25519 Ziw7aw W4nd317o0ON6n006hwUNIops3L7VngNqDqJ1bG7tCyg
+xyjvZOOzA0u3e+Cba99LR8J5JAkl6muHuspJ+b8dEog
+-> ssh-ed25519 uKftJg bX0GHUPdD4hR2yxLNx8ho689or7FNHXPA8iV9Af1q2s
+B91XIdsnHfAKdKfu8jmHKKptA5OomQ5sHvXfLLUeNbs
+--- 8zoH1w5ywsbDN5Xt50sE4BUgXoq12mr5b4rSVYMLEB8
+CŽb;*œã‚´*;í5œ#BL^ñƒT¯úE¢<45>%ÚÎçáZ8†r‰wݧ#‚r-îG¢éÖKÔ—t…|Ê
+pí³ÿÑòâÙ_ßÄÊ»\s»N´C‚UG
|º‡*i(6ÇÔA•k/µy

secrets/pi-to-cache-key.age

@@ -1,9 +1,11 @@
 age-encryption.org/v1
--> ssh-ed25519 Ziw7aw fWhlaYGRUca7VIr427vosdJGvOyWsywZrfhYRbV2hiU
-qUKuoolDRtKRs27nCSbzrDGO9q7JVuIK8LcyVlqFj/o
--> ssh-ed25519 jcT/MQ yEqLDa+E44c/PSY4bGCHKsJiPGcPUNxE5ihFUcBRwVI
-svHSjYLKfGvbQgQXk/P4yfo4Rh8iQP446iibaIz82Po
--> ssh-ed25519 uKftJg HC2fqTtYg6WDUUuXdMKwHRBvD+bDrwtiuTbNCzOUV1I
-5UX0bDfIjN2TXfZLBy7dmy8WUuoGBmkPrcx6EH2j0WA
---- uiiOp5m+x+lJR2mjawNrZgOtTs1F1EGaLKmre7BIopE
-¼×D<08>7|7@}TD>>[i˜’_äE~Ë»0…<30>Ö´ê<C2B4>ª–}0çþTã£ã.ìÝZšmò±Øb¶E|<®½ »ñýªjó.Ž
+-> ssh-ed25519 Ziw7aw TMz4xBHmy5btMk5ETWyvjZcjj0QwF3F6Iqt2QmkwVwk
+KvcY409ZakEUO7OrmDrwseMQv/w7i3B7uDiXjls/5qE
+-> ssh-ed25519 jcT/MQ Y5TqVlHy3fM+CmQIBu1x18C3wjHtRZCHJ9dhFyVAR0I
+WPqxEZrpAm0wLYT4s9e1uxSuDjhwUwIOL4BvDtvqytU
+-> X25519 ZqSHgIStt6Ru3osVvMA1M5sydoY+CeZ56temQyCFIVY
+4tPA6VITlAzJxCFGVreKK1B6rrHm+ka4ELwnzYrMKbQ
+-> ssh-ed25519 uKftJg OR8VgPUuEvS/0Gc5c92IlAp4DKKYcRzBbSh1tX9ddzg
+DZYYx9ngwEUTmj/JaP2XnCQHjpPY8WYgOEDlOfZPLeA
+--- 4iDfaqdSLiW0doVijoZC5ckxiCmsmVWJi5Kvaxic2Ng
+è÷VV;2†h<>&e@sÏx#d=Y?iðw½´ÉÍF<15>OÝc×/ûš(™¨àœ›¼føkØ틃—¿}
[¡¤'=B@ô‡¨Â!wÔ

secrets/secrets.nix

@@ -2,11 +2,33 @@ let
   jet = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIE40ISu3ydCqfdpb26JYD5cIN0Fu0id/FDS+xjB5zpqu";
   pi = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKmJFZAVJUjDziQ7XytVhQIv+Pm9hnbVU0flxZK17K5E";
   server = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAING219cDKTDLaZefmqvOHfXvYloA/ErsCGE0pM022vlB";
+  piBootstrap = "age1sfqn46dgztr35dtyhpzyzzam5m6kcqu495qs7fcsdxtac56pc4dsj3t862";
 in
 {
-  "pi-to-cache-key.age".publicKeys = [ jet pi server ];
-  "cache-to-pi-key.age".publicKeys = [ jet pi server ];
-  "tailscale-auth-key.age".publicKeys = [ jet pi ];
-  "discord-token.age".publicKeys = [ jet server ];
-  "discord-webhook-secret.age".publicKeys = [ jet server ];
+  "bootstrap-identity.age".publicKeys = [ jet ];
+  "pi-to-cache-key.age".publicKeys = [
+    jet
+    pi
+    piBootstrap
+    server
+  ];
+  "cache-to-pi-key.age".publicKeys = [
+    jet
+    pi
+    piBootstrap
+    server
+  ];
+  "tailscale-auth-key.age".publicKeys = [
+    jet
+    pi
+    piBootstrap
+  ];
+  "discord-token.age".publicKeys = [
+    jet
+    server
+  ];
+  "discord-webhook-secret.age".publicKeys = [
+    jet
+    server
+  ];
 }