test: add basic lib function tests for agents and coding-rules

tests/lib/agents-test.nix

@@ -0,0 +1,29 @@
+let
+  lib = import <nixpkgs/lib>;
+  agentsLib = (import ../../lib {inherit lib;}).agents;
+
+  # Test 1: renderForTool throws for unknown tools
+  testUnknownTool = let
+    result = builtins.tryEval (
+      agentsLib.renderForTool {
+        pkgs = {};
+        agentsInput = {};
+        tool = "unknown-tool";
+      }
+    );
+  in
+    assert result.success == false;
+    {result = "pass";};
+
+  # Test 2: loadCanonical extracts loadAgents from input
+  testLoadCanonical = let
+    fakeInput = {lib.loadAgents = {test = {description = "test";};};};
+    result = agentsLib.loadCanonical {agentsInput = fakeInput;};
+  in
+    assert result == {test = {description = "test";};};
+    {result = "pass";};
+
+in {
+  unknown-tool-throws = testUnknownTool;
+  load-canonical = testLoadCanonical;
+}