feat(sops): add sops-nix input, core module and devShell tooling

Wires sops-nix into every machine via machines/core/sops.nix so hosts
decrypt with their existing SSH host key. Adds a devShell exposing
sops/age/ssh-to-age for the operator workflow, which also fixes .envrc's
previously no-op `use flake`.

.gitignore

@@ -1 +1,3 @@
 AGENTS.md
+*.dec
+keys.txt

.sops.yaml

@@ -0,0 +1,17 @@
+keys:
+  - &admin_finn age1a0v442ct2qfjcdhyktn25spw02yq4fl08plrrvuradwwxzsle4mq8thln4
+  - &host_mibook age1n3uqtee5ymykrls6k04dznq50cwmj99hw7ny83yxjndt4y2ncf5qhjwa2p
+  # - &host_jupiter age1...   # TODO: Phase 9, see docs/secrets.md
+
+creation_rules:
+  - path_regex: ^secrets/mibook\.yaml$
+    key_groups:
+      - age:
+          - *admin_finn
+          - *host_mibook
+  # - path_regex: ^secrets/jupiter\.yaml$   # TODO: Phase 9
+  #   key_groups:
+  #     - age: [ *admin_finn, *host_jupiter ]
+  # - path_regex: ^secrets/common\.yaml$    # TODO: Phase 9
+  #   key_groups:
+  #     - age: [ *admin_finn, *host_mibook, *host_jupiter ]

flake.lock

@@ -264,7 +264,28 @@
         "nixos-generators": "nixos-generators",
         "nixos-hardware": "nixos-hardware",
         "nixpkgs": "nixpkgs_3",
-        "nixpkgs-unstable": "nixpkgs-unstable"
+        "nixpkgs-unstable": "nixpkgs-unstable",
+        "sops-nix": "sops-nix"
+      }
+    },
+    "sops-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1788337237,
+        "narHash": "sha256-gkSH8VUtCo6hnysNmb9DbTuDepH2t5pv+QWjP75xKAk=",
+        "owner": "Mic92",
+        "repo": "sops-nix",
+        "rev": "fbf759290e0cb0a98dfc813a4eb7d53ad1dacb57",
+        "type": "github"
+      },
+      "original": {
+        "owner": "Mic92",
+        "repo": "sops-nix",
+        "type": "github"
       }
     }
   },

flake.nix

@@ -11,6 +11,10 @@
       url = "github:nix-community/nixos-generators";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    sops-nix = {
+      url = "github:Mic92/sops-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
 
   };
 
@@ -36,6 +40,15 @@
           _module.args.pkgs = import inputs.nixpkgs {
             inherit system;
           };
+
+          devShells.default = pkgs.mkShell {
+            packages = with pkgs; [
+              sops
+              age
+              ssh-to-age
+              nixfmt
+            ];
+          };
         };
 
       systems = [ "x86_64-linux" ];

machines/configuration.nix

@@ -4,6 +4,7 @@ let
     nixpkgs
     nixpkgs-unstable
     nixos-hardware
+    sops-nix
     #hyprland
     ;
   nixosSystem = nixpkgs.lib.makeOverridable nixpkgs.lib.nixosSystem;
@@ -40,6 +41,7 @@ let
       ];
     }
     ../modules
+    sops-nix.nixosModules.sops
     # ../profiles
   ];
   defaultModules = baseModules ++ customModules;

machines/core/default.nix

@@ -3,5 +3,6 @@
   ./modules.nix
   ./network.nix
   ./nix.nix
+  ./sops.nix
   ./users.nix
 ]

machines/core/sops.nix

@@ -0,0 +1,31 @@
+# sops-nix plumbing — applied to every machine.
+# See docs/secrets.md for the day-to-day workflow.
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  # Each host defaults to its own secrets/<hostname>.yaml. Override per-secret
+  # with sops.secrets.<name>.sopsFile for shared files.
+  sops.defaultSopsFile = lib.mkDefault (../../secrets + "/${config.networking.hostName}.yaml");
+  sops.defaultSopsFormat = "yaml";
+  sops.validateSopsFiles = true;
+
+  # Decrypt with the host's own SSH host key, converted to age.
+  # Explicit rather than inheriting the openssh-derived default, so this does
+  # not silently break if services.openssh is ever disabled.
+  sops.age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
+  sops.age.generateKey = false;
+
+  # Age only. The default here is the RSA host key imported as a GPG key,
+  # which is deprecated and an extra failure surface.
+  sops.gnupg.sshKeyPaths = [ ];
+
+  environment.systemPackages = with pkgs; [
+    sops
+    age
+    ssh-to-age
+  ];
+}