feat(genui): support functions in prompts and verify rendering

dev_tools/composer/lib/create_tab.dart

@@ -78,7 +78,7 @@ class _CreateTabState extends State<CreateTab> {
         transport: transport,
       );
 
-      final promptBuilder = PromptBuilder.chat(
+      final promptBuilder = await PromptBuilder.createChat(
         catalog: catalog,
         systemPromptFragments: [
           'You are a UI generator. The user will describe a UI they want. '

examples/simple_chat/lib/chat_session.dart

@@ -56,19 +56,20 @@ final Catalog _customCatalog = _basicCatalog.copyWith(
   newItems: [climbingLocationItem],
 );
 
-PromptBuilder _promptBuilderFor(Catalog catalog) => PromptBuilder.chat(
-  catalog: catalog,
-  systemPromptFragments: [
-    Prompts.summary,
-    PromptFragments.acknowledgeUser(),
-    PromptFragments.requireAtLeastOneSubmitElement(
-      prefix: PromptBuilder.defaultImportancePrefix,
-    ),
-    PromptFragments.uiGenerationRestriction(
-      prefix: PromptBuilder.defaultImportancePrefix,
-    ),
-  ],
-);
+Future<PromptBuilder> _promptBuilderFor(Catalog catalog) async =>
+    await PromptBuilder.createChat(
+      catalog: catalog,
+      systemPromptFragments: [
+        Prompts.summary,
+        PromptFragments.acknowledgeUser(),
+        PromptFragments.requireAtLeastOneSubmitElement(
+          prefix: PromptBuilder.defaultImportancePrefix,
+        ),
+        PromptFragments.uiGenerationRestriction(
+          prefix: PromptBuilder.defaultImportancePrefix,
+        ),
+      ],
+    );
 
 sealed class ChatSession extends ChangeNotifier {
   ChatSession._();
@@ -188,7 +189,7 @@ class A2uiChatSession extends ChatSession {
   late final StreamSubscription<ChatMessage> _submitSub;
   late final StreamSubscription<SurfaceUpdate> _surfaceSub;
 
-  void _init() {
+  Future<void> _init() async {
     _messageSub = _transport.incomingMessages.listen(
       _surfaceController.handleMessage,
     );
@@ -198,9 +199,8 @@ class A2uiChatSession extends ChatSession {
     );
     _surfaceSub = _surfaceController.surfaceUpdates.listen(_onSurfaceUpdate);
 
-    _transport.addSystemMessage(
-      _promptBuilderFor(_catalog).systemPromptJoined(),
-    );
+    final PromptBuilder pb = await _promptBuilderFor(_catalog);
+    _transport.addSystemMessage(pb.systemPromptJoined());
   }
 
   void _onSurfaceUpdate(SurfaceUpdate update) {

examples/verdure/client/linux/flutter/generated_plugins.cmake

@@ -9,6 +9,7 @@ list(APPEND FLUTTER_PLUGIN_LIST
 )
 
 list(APPEND FLUTTER_FFI_PLUGIN_LIST
+  jni
 )
 
 set(PLUGIN_BUNDLED_LIBRARIES)

examples/verdure/client/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -16,5 +16,5 @@ func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   DeviceInfoPlusMacosPlugin.register(with: registry.registrar(forPlugin: "DeviceInfoPlusMacosPlugin"))
   FileSelectorPlugin.register(with: registry.registrar(forPlugin: "FileSelectorPlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))
-  FVPVideoPlayerPlugin.register(with: registry.registrar(forPlugin: "FVPVideoPlayerPlugin"))
+  VideoPlayerPlugin.register(with: registry.registrar(forPlugin: "VideoPlayerPlugin"))
 }

packages/genui/assets/schemas/common_types.json

@@ -0,0 +1 @@
+../../../../submodules/a2ui/specification/v0_9/json/common_types.json

packages/genui/assets/schemas/server_to_client.json

@@ -0,0 +1 @@
+../../../../submodules/a2ui/specification/v0_9/json/server_to_client.json

packages/genui/lib/src/catalog/basic_catalog_widgets/button.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/material.dart';
 import 'package:json_schema_builder/json_schema_builder.dart';
 
+import '../../model/a2ui_exceptions.dart';
 import '../../model/a2ui_schemas.dart';
 import '../../model/catalog_item.dart';
 import '../../model/data_model.dart';
@@ -233,7 +234,33 @@ Future<void> _handlePress(
     try {
       await resultStream.first;
     } catch (exception, stackTrace) {
-      itemContext.reportError(exception, stackTrace);
+      genUiLogger.severe(
+        'Error executing function call "$callName" on button press',
+        exception,
+        stackTrace,
+      );
+
+      if (exception is A2uiFunctionException) {
+        itemContext.reportError(exception, stackTrace);
+      } else if (exception is ArgumentError) {
+        itemContext.reportError(
+          A2uiFunctionException(
+            exception.message.toString(),
+            functionName: callName,
+            cause: exception,
+          ),
+          stackTrace,
+        );
+      } else {
+        itemContext.reportError(
+          A2uiFunctionException(
+            'Function execution failed. Please check arguments and try again.',
+            functionName: callName,
+            cause: exception,
+          ),
+          stackTrace,
+        );
+      }
     }
   } else {
     genUiLogger.warning(

packages/genui/lib/src/catalog/basic_catalog_widgets/date_time_input.dart

@@ -340,9 +340,7 @@ final dateTimeInput = CatalogItem(
         {
           "id": "root",
           "component": "DateTimeInput",
-          "value": {
-            "path": "/myDateTime"
-          }
+          "value": "2026-05-15"
         }
       ]
     ''',
@@ -354,7 +352,7 @@ final dateTimeInput = CatalogItem(
           "value": {
             "path": "/myDate"
           },
-          "enableTime": false
+          "variant": "date"
         }
       ]
     ''',
@@ -366,7 +364,7 @@ final dateTimeInput = CatalogItem(
           "value": {
             "path": "/myTime"
           },
-          "enableDate": false
+          "variant": "time"
         }
       ]
     ''',

packages/genui/lib/src/catalog/basic_catalog_widgets/image.dart

@@ -78,7 +78,9 @@ final CatalogItem image = CatalogItem(
       {
         "id": "root",
         "component": "Image",
-        "url": "https://storage.googleapis.com/cms-storage-bucket/lockup_flutter_horizontal.c823e53b3a1a7b0d36a9.png",
+        "url": {
+          "path": "/imageUrl"
+        },
         "variant": "mediumFeature"
       }
     ]

packages/genui/lib/src/catalog/basic_catalog_widgets/text.dart

@@ -52,8 +52,7 @@ final text = CatalogItem(
         {
           "id": "root",
           "component": "Text",
-          "text": "Hello World",
-          "variant": "h1"
+          "text": "Hello World"
         }
       ]
     ''',

packages/genui/lib/src/engine/surface_controller.dart

@@ -12,6 +12,7 @@ import '../interfaces/a2ui_message_sink.dart';
 import '../interfaces/surface_context.dart';
 import '../interfaces/surface_host.dart';
 import '../model/a2ui_client_capabilities.dart';
+import '../model/a2ui_exceptions.dart';
 import '../model/a2ui_message.dart';
 import '../model/catalog.dart';
 import '../model/chat_message.dart';
@@ -120,16 +121,21 @@ interface class SurfaceController implements SurfaceHost, A2uiMessageSink {
 
   /// Reports an error to the AI service.
   void reportError(Object error, StackTrace? stack) {
-    var errorCode = 'RUNTIME_ERROR';
-    var message = error.toString();
+    var errorCode = 'INTERNAL_ERROR';
+    var message = 'An unexpected system error occurred.';
     String? surfaceId;
     String? path;
+    String? functionName;
 
     if (error is A2uiValidationException) {
       errorCode = 'VALIDATION_FAILED';
       message = error.message;
       surfaceId = error.surfaceId;
       path = error.path;
+    } else if (error is A2uiFunctionException) {
+      errorCode = 'FUNCTION_EXECUTION_FAILED';
+      message = error.message;
+      functionName = error.functionName;
     }
 
     final Map<String, Object> errorMsg = {
@@ -138,15 +144,18 @@ interface class SurfaceController implements SurfaceHost, A2uiMessageSink {
         'code': errorCode,
         'surfaceId': ?surfaceId,
         'path': ?path,
+        'functionName': ?functionName,
         'message': message,
       },
     };
-    _onSubmit.add(
-      ChatMessage.user(
-        '',
-        parts: [UiInteractionPart.create(jsonEncode(errorMsg))],
-      ),
-    );
+    if (!_onSubmit.isClosed) {
+      _onSubmit.add(
+        ChatMessage.user(
+          '',
+          parts: [UiInteractionPart.create(jsonEncode(errorMsg))],
+        ),
+      );
+    }
   }
 
   void _handleMessageInternal(A2uiMessage message) {