fixed

src/client/Cosmetic.ts

@@ -51,7 +51,7 @@ export class PatternDecoder {
       height > 63
     ) {
       throw new Error(
-        "Scale must be 1–128, width must be 1–127, and height must be 1–63.",
+        `Invalid pattern metadata: scale (log₂)=${scale}, width=${width}, height=${height}. Expected: scale 0–7, width 1–127, height 1–63.`,
       );
     }
 

src/client/TerritoryPatternsModal.ts

@@ -219,7 +219,10 @@ export class TerritoryPatternsModal extends LitElement {
     const cellCountX = decoder.getTileWidth();
     const cellCountY = decoder.getTileHeight();
 
-    const cellSize = Math.min(height / cellCountY, width / cellCountX);
+    const cellSize =
+      cellCountX > 0 && cellCountY > 0
+        ? Math.min(height / cellCountY, width / cellCountX)
+        : 1;
 
     return html`
       <div