secrets overhaul: use tpm for laptop (need to migrate desktop later)

modules/desktop-age-secrets.nix

@@ -0,0 +1,70 @@
+{
+  pkgs,
+  inputs,
+  ...
+}:
+let
+  # rage cannot invoke age-plugin-tpm unless the plugin binary is on PATH at
+  # activation time. Wrap rage so the activation scripts (and anything else
+  # that picks up `age.ageBin`) get age-plugin-tpm for free.
+  rageWithTpm = pkgs.writeShellScriptBin "rage" ''
+    export PATH="${pkgs.age-plugin-tpm}/bin:$PATH"
+    exec ${pkgs.rage}/bin/rage "$@"
+  '';
+in
+{
+  imports = [
+    inputs.agenix.nixosModules.default
+  ];
+
+  # Expose the plugin + agenix CLI for interactive edits (`agenix -e …`).
+  environment.systemPackages = [
+    inputs.agenix.packages.${pkgs.system}.default
+    pkgs.age-plugin-tpm
+  ];
+
+  age.ageBin = "${rageWithTpm}/bin/rage";
+
+  # Primary identity: TPM-sealed key, generated by scripts/bootstrap-desktop-tpm.sh.
+  # Fallback identity: admin SSH key. age tries paths in order, so if the TPM
+  # is wiped or the board is replaced the SSH key keeps secrets accessible until
+  # the TPM is re-bootstrapped. Both are encrypted recipients on every .age file.
+  age.identityPaths = [
+    "/var/lib/agenix/tpm-identity"
+    "/home/primary/.ssh/id_ed25519"
+  ];
+
+  # Ensure the identity directory exists before agenix activation so a fresh
+  # bootstrap doesn't race the directory creation.
+  systemd.tmpfiles.rules = [
+    "d /var/lib/agenix 0700 root root -"
+  ];
+
+  age.secrets = {
+    # Secureboot PKI bundle (db/KEK/PK keys + certs) consumed by lanzaboote
+    # via desktop-lanzaboote-agenix.nix at activation time.
+    secureboot-tar = {
+      file = ../secrets/desktop/secureboot.tar.age;
+      mode = "0400";
+      owner = "root";
+      group = "root";
+    };
+
+    # netrc for the private nix binary cache.
+    nix-cache-netrc = {
+      file = ../secrets/desktop/nix-cache-netrc.age;
+      mode = "0400";
+      owner = "root";
+      group = "root";
+    };
+
+    # yescrypt hash for the primary user.
+    password-hash = {
+      file = ../secrets/desktop/password-hash.age;
+      mode = "0400";
+      owner = "root";
+      group = "root";
+    };
+
+  };
+}