rework

effects.cm

@@ -92,7 +92,8 @@ effects.register('mask', {
   type: 'conditional',
   requires_target: true,
   params: {
-    source: {required: true},
+    source: {required: false},  // Legacy: direct handle reference
+    source_id: {required: false}, // New: ID string for film2d.get()
     channel: {default: 'alpha'},
     invert: {default: false},
     soft: {default: false},
@@ -112,11 +113,22 @@ effects.register('mask', {
       return [{type: 'blit', source: input, dest: output}]
     }
 
+    // Resolve mask source
+    var mask_source = params.source
+    if (params.source_id && ctx.film2d) {
+      mask_source = ctx.film2d.get(params.source_id)
+    }
+
+    if (!mask_source) {
+      // No mask source - pass through
+      return [{type: 'blit', source: input, dest: output}]
+    }
+
     // Render mask source to target
     var mask_target = ctx.alloc_target(size.width, size.height, 'mask_src')
     passes.push({
       type: 'render_subtree',
-      root: params.source,
+      root: mask_source,
       output: mask_target,
       clear: {r: 0, g: 0, b: 0, a: 0},
       space: params.space || 'local'