From 6b0b637636174e670199e5a8fb6679ab5a536a6b Mon Sep 17 00:00:00 2001
From: Leopoldadmin <leopold.hammerschmidt@media-on.de>
Date: Mon, 29 Jun 2026 00:34:39 +0200
Subject: [PATCH] fix: collab sync no longer overwrites layers with empty array

- Root cause: App.tsx collab sync effect called setLayers(collab.layers)
  even when collab.layers was empty, wiping out initialLayers
- Effect: RenderEngine.render() iterates layers to draw elements;
  with 0 layers, no elements render (appear to disappear)
- Fix: guard against empty collab.layers

Fixes: drawing tools work on desktop and mobile, objects persist after release
---
 frontend/src/App.tsx | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 0dd05e5..2b77f01 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -299,9 +299,12 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
       setElements(merged);
     }
 
-    const sameLayers = collab.layers.length === layers.length &&
-      collab.layers.every((l, i) => l.id === layers[i]?.id);
-    if (!sameLayers) setLayers(collab.layers);
+    // Never overwrite local layers with empty remote layers (prevents losing initialLayers)
+    if (collab.layers.length > 0) {
+      const sameLayers = collab.layers.length === layers.length &&
+        collab.layers.every((l, i) => l.id === layers[i]?.id);
+      if (!sameLayers) setLayers(collab.layers);
+    }
 
     const sameBlocks = collab.blocks.length === blocks.length &&
       collab.blocks.every((b, i) => b.id === blocks[i]?.id);