test: add TestCallPluginFunction + final run - all 13 tests pass

- TestCallPluginFunction: verifies DoString calls Lua functions correctly
  - add(3,4) → 7, greet('World') → 'Hello, World', get_table() → table
- Full suite: 13 tests, 0 failures
- go build ./... clean

internal/core/plugins/runtime_test.go

@@ -390,3 +390,86 @@ func copyDir(src, dst string) error {
 		return os.WriteFile(target, data, info.Mode())
 	})
 }
+
+// TestCallPluginFunction verifies that DoString can call Lua functions
+// and return results through the VM.
+func TestCallPluginFunction(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create a simple plugin with a global function
+	pluginDir := filepath.Join(dir, "testfunc")
+	if err := os.MkdirAll(pluginDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	luaCode := `
+function add(a, b)
+  return a + b
+end
+
+function greet(name)
+  return "Hello, " .. name
+end
+
+function get_table()
+  return { x = 42, y = "test" }
+end
+`
+	if err := os.WriteFile(filepath.Join(pluginDir, "main.lua"), []byte(luaCode), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	p := &Plugin{
+		Meta: Meta{
+			Name: "testfunc",
+			Hooks: map[string]string{
+				"on_install": "on_install",
+			},
+		},
+		Dir:      pluginDir,
+		DataDir:  filepath.Join(dir, "data"),
+		Active:   true,
+		HasInstall: true,
+	}
+	os.MkdirAll(p.DataDir, 0755)
+
+	vm, err := NewLuaVM(p)
+	if err != nil {
+		t.Fatalf("NewLuaVM: %v", err)
+	}
+	defer vm.Close()
+
+	// Load main.lua
+	if err := vm.LoadScript("main.lua"); err != nil {
+		t.Fatalf("LoadScript: %v", err)
+	}
+
+	// Test 1: add(3, 4) → "7"
+	result, err := vm.DoString("return add(3, 4)")
+	if err != nil {
+		t.Fatalf("DoString(add): %v", err)
+	}
+	if result != "7" {
+		t.Errorf("add(3,4) = %q, want %q", result, "7")
+	}
+
+	// Test 2: greet("World") → "Hello, World"
+	result, err = vm.DoString("return greet('World')")
+	if err != nil {
+		t.Fatalf("DoString(greet): %v", err)
+	}
+	if result != "Hello, World" {
+		t.Errorf("greet('World') = %q, want %q", result, "Hello, World")
+	}
+
+	// Test 3: get_table() → table string (just verify no error)
+	result, err = vm.DoString("return get_table()")
+	if err != nil {
+		t.Fatalf("DoString(get_table): %v", err)
+	}
+	if result == "" || result == "nil" {
+		t.Errorf("get_table() returned empty/nil: %q", result)
+	}
+
+	t.Logf("DoString tests passed: add=%q, greet=%q, get_table=%q", result, result, result)
+}