refactor: centralize agent skills at ~/.agents/skills

modules/home-manager/coding/agents/default.nix

@@ -1,10 +1,39 @@
 # Per-tool agent sub-modules
 # Each module handles rendering canonical agent.toml definitions
 # for a specific AI coding tool.
+#
+# Also provides the shared coding.agents.skills submodule that writes
+# ~/.agents/skills — the central skills directory used by Pi, OpenCode, etc.
 {
+  config,
+  lib,
+  pkgs,
+  ...
+}: let
+  shared = import ./shared-options.nix {inherit lib;};
+  cfg = config.coding.agents.skills;
+  mkIf = lib.mkIf;
+in {
   imports = [
     ./opencode.nix
     ./claude-code.nix
     ./pi.nix
   ];
+
+  options.coding.agents.skills = {
+    agentsInput = shared.mkAgentsInputOption ''
+      The `agents` flake input (your personal AGENTS repo).
+      When set, skills are symlinked to ~/.agents/skills.
+    '';
+
+    externalSkills = shared.externalSkillsOption;
+  };
+
+  config = mkIf (cfg.agentsInput != null) {
+    home.file.".agents/skills".source = cfg.agentsInput.lib.mkOpencodeSkills {
+      inherit pkgs;
+      customSkills = "${cfg.agentsInput}/skills";
+      externalSkills = shared.mapExternalSkills cfg.externalSkills;
+    };
+  };
 }