Fix text alpha updates during fade

lib/runtime/rendering/runtime_component.dart

@@ -67,7 +67,12 @@ class RuntimeComponent extends PositionComponent
   double get renderAlpha => _runtimeAlpha ?? _node.alpha;
 
   void setRuntimeAlpha(double value) {
-    _runtimeAlpha = value.clamp(0, 1).toDouble();
+    final next = value.clamp(0, 1).toDouble();
+    if (_runtimeAlpha == next) {
+      return;
+    }
+    _runtimeAlpha = next;
+    _syncTextStyle(_node);
   }
 
   void setParentScroll({
@@ -961,21 +966,11 @@ class RuntimeComponent extends PositionComponent
     }
 
     final text = label ?? '';
-    final color = _textColor(node);
-    final style = TextStyle(
-      color: composeRuntimeColorAlpha(color, renderAlpha),
-      fontSize: node.fontSize ?? 18,
-      fontWeight: node.type == RuntimeNodeType.button
-          ? FontWeight.w600
-          : FontWeight.normal,
-      shadows: _textShadows(node),
-    );
-
     final component = _textComponent;
     if (component == null) {
       _textComponent = TextComponent(
         text: text,
-        textRenderer: TextPaint(style: style),
+        textRenderer: TextPaint(style: _textStyle(node)),
         anchor: _textAnchor(node),
         position: _textPosition(node),
         priority: priority + 1,
@@ -986,10 +981,30 @@ class RuntimeComponent extends PositionComponent
 
     component
       ..text = text
-      ..textRenderer = TextPaint(style: style)
       ..anchor = _textAnchor(node)
       ..position = _textPosition(node)
       ..priority = priority + 1;
+    _syncTextStyle(node);
+  }
+
+  void _syncTextStyle(RuntimeNode node) {
+    final component = _textComponent;
+    if (component == null) {
+      return;
+    }
+    component.textRenderer = TextPaint(style: _textStyle(node));
+  }
+
+  TextStyle _textStyle(RuntimeNode node) {
+    final color = _textColor(node);
+    return TextStyle(
+      color: composeRuntimeColorAlpha(color, renderAlpha),
+      fontSize: node.fontSize ?? 18,
+      fontWeight: node.type == RuntimeNodeType.button
+          ? FontWeight.w600
+          : FontWeight.normal,
+      shadows: _textShadows(node),
+    );
   }
 
   @override

test/runtime/rendering/runtime_component_test.dart

@@ -138,6 +138,51 @@ void main() {
       );
     });
 
+    test('updates text alpha style without rebuilding text component', () {
+      final component = RuntimeComponent(
+        node: const RuntimeNode(
+          id: 'text',
+          type: RuntimeNodeType.text,
+          text: 'Fade me',
+          alpha: 0,
+          color: Color(0xffffffff),
+        ),
+        resources: GameResourceManager(),
+        onNodeTap: (_, __) {},
+      );
+
+      final text = component.children.whereType<TextComponent>().single;
+      expect(((text.textRenderer as TextPaint).style.color!).a, 0);
+
+      component.setRuntimeAlpha(1);
+
+      final updatedText = component.children.whereType<TextComponent>().single;
+      expect(identical(updatedText, text), isTrue);
+      expect(((updatedText.textRenderer as TextPaint).style.color!).a, 1);
+    });
+
+    test('updates button text alpha style without rebuilding text component', () {
+      final component = RuntimeComponent(
+        node: const RuntimeNode(
+          id: 'button',
+          type: RuntimeNodeType.button,
+          text: 'Fade me',
+          alpha: 0,
+        ),
+        resources: GameResourceManager(),
+        onNodeTap: (_, __) {},
+      );
+
+      final text = component.children.whereType<TextComponent>().single;
+      expect(((text.textRenderer as TextPaint).style.color!).a, 0);
+
+      component.setRuntimeAlpha(1);
+
+      final updatedText = component.children.whereType<TextComponent>().single;
+      expect(identical(updatedText, text), isTrue);
+      expect(((updatedText.textRenderer as TextPaint).style.color!).a, 1);
+    });
+
     test('applies text shadow style', () {
       final component = RuntimeComponent(
         node: const RuntimeNode(