feat(api): fall back to group tags in openapi

Co-Authored-By: Virgil <virgil@lethean.io>

openapi.go

@@ -108,7 +108,7 @@ func (sb *SpecBuilder) buildPaths(groups []RouteGroup) map[string]any {
 			operation := map[string]any{
 				"summary":     rd.Summary,
 				"description": rd.Description,
-				"tags":        rd.Tags,
+				"tags":        resolvedOperationTags(g, rd),
 				"operationId": operationID(method, fullPath, operationIDs),
 				"security": []any{
 					map[string]any{
@@ -191,6 +191,20 @@ func (sb *SpecBuilder) buildTags(groups []RouteGroup) []map[string]any {
 	return tags
 }
 
+// resolvedOperationTags returns the explicit route tags when provided, or a
+// stable fallback derived from the group's name when the route omits tags.
+func resolvedOperationTags(g RouteGroup, rd RouteDescription) []string {
+	if len(rd.Tags) > 0 {
+		return rd.Tags
+	}
+
+	if name := g.Name(); name != "" {
+		return []string{name}
+	}
+
+	return nil
+}
+
 // envelopeSchema wraps a data schema in the standard Response[T] envelope.
 func envelopeSchema(dataSchema map[string]any) map[string]any {
 	properties := map[string]any{

openapi_test.go

@@ -468,6 +468,47 @@ func TestSpecBuilder_Good_NonDescribableGroup(t *testing.T) {
 	}
 }
 
+func TestSpecBuilder_Good_DefaultTagsFromGroupName(t *testing.T) {
+	sb := &api.SpecBuilder{
+		Title:   "Test",
+		Version: "1.0.0",
+	}
+
+	group := &specStubGroup{
+		name:     "fallback",
+		basePath: "/api/fallback",
+		descs: []api.RouteDescription{
+			{
+				Method:  "GET",
+				Path:    "/status",
+				Summary: "Check status",
+				Response: map[string]any{
+					"type": "object",
+				},
+			},
+		},
+	}
+
+	data, err := sb.Build([]api.RouteGroup{group})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var spec map[string]any
+	if err := json.Unmarshal(data, &spec); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+
+	operation := spec["paths"].(map[string]any)["/api/fallback/status"].(map[string]any)["get"].(map[string]any)
+	tags, ok := operation["tags"].([]any)
+	if !ok {
+		t.Fatalf("expected tags array, got %T", operation["tags"])
+	}
+	if len(tags) != 1 || tags[0] != "fallback" {
+		t.Fatalf("expected fallback tag from group name, got %v", operation["tags"])
+	}
+}
+
 func TestSpecBuilder_Good_ToolBridgeIntegration(t *testing.T) {
 	gin.SetMode(gin.TestMode)