feat(agent-skills): wire skills flake for global agent skills

Add the skills flake as an input and a module that imports its
home-manager module into every host via home-manager.sharedModules,
exposing programs.agents.skills. The global skill selection lives in
modules/agent-skills.nix and is empty for now; per-skill granularity
comes from the flake's own listOf-package option, and the placement
self-gates on the agent harness being enabled.

flake.lock

@@ -181,6 +181,24 @@
         "url": "https://flakehub.com/f/DeterminateSystems/flake-schemas/%3D0.5.0.tar.gz"
       }
     },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems_2"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
     "fromYaml": {
       "flake": false,
       "locked": {
@@ -299,6 +317,27 @@
         "type": "github"
       }
     },
+    "home-manager_4": {
+      "inputs": {
+        "nixpkgs": [
+          "skills",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1784725727,
+        "narHash": "sha256-J5+C9wsO0lhDyUalQzfplDbRjyHDYeEH5+9sdyXtwa8=",
+        "owner": "nix-community",
+        "repo": "home-manager",
+        "rev": "041a999e8c1c5b731913855909e68d30ca69b8e0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "home-manager",
+        "type": "github"
+      }
+    },
     "nixos-hardware": {
       "inputs": {
         "nixpkgs": [
@@ -441,10 +480,33 @@
         "nixpkgs-stable": "nixpkgs-stable",
         "nixpkgs-unstable": "nixpkgs-unstable",
         "nixvim": "nixvim",
+        "skills": "skills",
         "sops-nix": "sops-nix",
         "stylix": "stylix"
       }
     },
+    "skills": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "home-manager": "home-manager_4",
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1784776947,
+        "narHash": "sha256-IGVn6Z7dfeArObZvz7cLsGqJD8ipP2VkAZC/bOJgvJI=",
+        "ref": "refs/heads/main",
+        "rev": "1caf18d72dd7cad7304401da0db6a6ba853d8827",
+        "revCount": 5,
+        "type": "git",
+        "url": "https://git.alexion.dev/alexion/skills"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://git.alexion.dev/alexion/skills"
+      }
+    },
     "sops-nix": {
       "inputs": {
         "nixpkgs": [
@@ -478,7 +540,7 @@
           "nixpkgs"
         ],
         "nur": "nur",
-        "systems": "systems_2",
+        "systems": "systems_3",
         "tinted-kitty": "tinted-kitty",
         "tinted-schemes": "tinted-schemes",
         "tinted-tmux": "tinted-tmux",
@@ -529,6 +591,21 @@
         "type": "github"
       }
     },
+    "systems_3": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
     "tinted-kitty": {
       "flake": false,
       "locked": {

flake.nix

@@ -54,6 +54,13 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
 
+    # Personal agent skills, packaged as per-skill derivations with a
+    # home-manager module that places them under Claude Code's skills directory.
+    skills = {
+      url = "git+https://git.alexion.dev/alexion/skills";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     # CachyOS kernel and binary cache. Pins its own nixpkgs so its cache stays
     # usable and the kernel is fetched from it.
     chaotic.url = "github:chaotic-cx/nyx/nyxpkgs-unstable";

modules/agent-skills.nix

@@ -0,0 +1,15 @@
+{ config, inputs, ... }:
+# Global agent skills from the skills flake, placed under the agent harness's
+# skills directory so they are active in every project. The flake's home-manager
+# module self-gates on the harness being enabled and installs nothing for an
+# empty selection, so a host without one carries no skills either way.
+let
+  user = config.user.name;
+
+  # The skills installed globally, as derivations from the skills flake.
+  skills = [ ];
+in
+{
+  home-manager.sharedModules = [ inputs.skills.homeModules.default ];
+  home-manager.users.${user}.programs.agents.skills = skills;
+}