Image export: surface rasterize/serialize failures instead of reporting 'not ready'

src/app/components/LivePreview.tsx

@@ -342,8 +342,11 @@ export function LivePreview() {
   ]);
 
   // Rasterize/serialize the live view for the per-chart export (spec §08). Reads
-  // `handleRef` (the view LivePreview owns); returns null when no view is live or
-  // the export fails, so the export UI can report it. Stable identity (no deps).
+  // `handleRef` (the view LivePreview owns); returns null only when no view is live
+  // (the "not ready" case). A rasterize/serialize *failure* is a real error, not a
+  // not-ready state, so it propagates for the export UI to report with its detail —
+  // burying it here would misreport a tainted canvas or a serialization bug as
+  // "not ready yet" (arch 02 fail-loud). Stable identity (no deps).
   const getImageUrl = useCallback(
     async (
       format: 'png' | 'svg',
@@ -351,11 +354,7 @@ export function LivePreview() {
     ): Promise<string | null> => {
       const handle = handleRef.current;
       if (!handle) return null;
-      try {
-        return await handle.toImageURL(format, options);
-      } catch {
-        return null;
-      }
+      return await handle.toImageURL(format, options);
     },
     [],
   );