Enforce explicit WebGL book playback timeline

public/js/playback-coordinator-module.js

@@ -252,16 +252,6 @@ class PlaybackCoordinatorModule extends BaseModule {
                 };
             });
         }
-        document.dispatchEvent(new CustomEvent('book-texture:reveal-block', {
-            detail: {
-                id: sentence.id,
-                blockId: sentence.blockId ?? sentence.metadata?.blockId ?? null,
-                wordTimings,
-                cueTimings,
-                totalDuration: sentence.animation.totalDuration || 0
-            }
-        }));
-
         return new Promise((resolve) => {
             const totalDuration = wordTimings.length > 0
                 ? Math.max(...wordTimings.map(timing => timing.delay + timing.duration))
@@ -332,15 +322,16 @@ class PlaybackCoordinatorModule extends BaseModule {
             cueTimings = [];
         }
 
-        document.dispatchEvent(new CustomEvent('book-texture:reveal-block', {
-            detail: {
-                id: sentence.id,
-                blockId: sentence.blockId ?? sentence.metadata?.blockId ?? null,
-                wordTimings,
-                cueTimings,
-                totalDuration: sentence.animation?.totalDuration || 0
-            }
-        }));
+        if (typeof sentence.webglRevealController !== 'function') {
+            throw new Error('PlaybackCoordinator: WebGL playback requires a prepared timeline reveal controller');
+        }
+        sentence.webglRevealController({
+            id: sentence.id,
+            blockId: sentence.blockId ?? sentence.metadata?.blockId ?? null,
+            wordTimings,
+            cueTimings,
+            totalDuration: sentence.animation?.totalDuration || 0
+        });
 
         return new Promise((resolve) => {
             const totalDuration = wordTimings.length > 0