feat(xai): support namespace tools and enhance tool normalization logic

- Added `namespace` tool type support, enabling nested tools to be normalized and moved to the top level.
- Refactored tool normalization logic into `normalizeXAITool` for reusability and clarity.
- Updated `xai_executor` test cases to validate namespace tool handling and nested tool normalization.

internal/registry/model_definitions_test.go

@@ -49,6 +49,42 @@ func TestWithXAIBuiltinsAddsVideoModel(t *testing.T) {
 	}
 }
 
+func TestValidateModelsCatalogAllowsMissingSections(t *testing.T) {
+	data := validTestModelsCatalog()
+	data.XAI = nil
+
+	if err := validateModelsCatalog(data); err != nil {
+		t.Fatalf("validateModelsCatalog() error = %v", err)
+	}
+}
+
+func TestValidateModelsCatalogRejectsInvalidDefinitions(t *testing.T) {
+	data := validTestModelsCatalog()
+	data.Claude = []*ModelInfo{{ID: ""}}
+
+	if err := validateModelsCatalog(data); err == nil {
+		t.Fatal("expected invalid model definition error")
+	}
+}
+
+func validTestModelsCatalog() *staticModelsJSON {
+	models := []*ModelInfo{{ID: "test-model"}}
+	return &staticModelsJSON{
+		Claude:      models,
+		Gemini:      models,
+		Vertex:      models,
+		GeminiCLI:   models,
+		AIStudio:    models,
+		CodexFree:   models,
+		CodexTeam:   models,
+		CodexPlus:   models,
+		CodexPro:    models,
+		Kimi:        models,
+		Antigravity: models,
+		XAI:         models,
+	}
+}
+
 func findModelInfo(models []*ModelInfo, id string) *ModelInfo {
 	for _, model := range models {
 		if model != nil && model.ID == id {

internal/registry/model_updater.go

@@ -349,7 +349,8 @@ func validateModelsCatalog(data *staticModelsJSON) error {
 
 func validateModelSection(section string, models []*ModelInfo) error {
 	if len(models) == 0 {
-		return fmt.Errorf("%s section is empty", section)
+		log.Warnf("models catalog: %s section is empty, continuing without those model definitions", section)
+		return nil
 	}
 
 	seen := make(map[string]struct{}, len(models))