#3478 [GUI] Persistent "Some model files are missing" error when loading Qwen3.6-35B-A3B (UD-Q4_K_XL)

Beschreibung

### **System Information**
* **OS:** Windows 11 
* **GPU:** NVIDIA GeForce RTX 3060 (12 GB VRAM)
* **RAM:** 32 GB

### **Description**
When trying to load the `Qwen3.6-35B-A3B` model (`UD-Q4_K_XL`), Strata displays an error stating: 
`Some model files are missing. Use Download / repair to restore them.` 

Clicking **Retry** or **Download & load** does not successfully download or repair the missing companion files/shards, leaving the model in an unusable state.

### **To Reproduce**
1. Open Strata and select the `Qwen3.6-35B-A3B` model (`UD-Q4_K_XL`).
2. Observe the missing model files error banner.
3. Click **Retry** or **Download & load**.
4. The error persists.

### **Expected Behavior**
Strata should automatically fetch and restore the required companion files, shards, or draft layers when clicking download or retry.

### **Screenshots**

<img width="883" height="576" alt="Image" src="https://github.com/user-attachments/assets/2877977b-c3e7-441e-beb9-2d92922f091a" />