fix: attach componentStack as string so ErrorBoundary works on React Native

spec/ErrorBoundary.spec.tsx

@@ -152,6 +152,23 @@ describe('<ErrorBoundary />', () => {
         await waitFor(() => expect(mockPost).toHaveBeenCalledTimes(1));
       });
 
+      it('should attach componentStack as a plain string (React Native friendly)', async () => {
+        render(
+          <ErrorBoundary scope={scope} fallback={BasicFallback}>
+            <BlowUp />
+          </ErrorBoundary>
+        );
+
+        await waitFor(() => expect(mockPost).toHaveBeenCalledTimes(1));
+
+        const [, options] = mockPost.mock.calls[0];
+        expect(options.attachments).toHaveLength(1);
+        const [attachment] = options.attachments;
+        expect(attachment.filename).toBe('componentStack.txt');
+        expect(typeof attachment.data).toBe('string');
+        expect(attachment.data).toContain('BlowUp');
+      });
+
       it('should call beforePost', async () => {
         render(
           <ErrorBoundary

src/ErrorBoundary.tsx

@@ -29,14 +29,19 @@ function isArrayDiff(a: unknown[] = [], b: unknown[] = []) {
 }
 
 /**
- * Pack a component stack trace string into an attachment
+ * Pack a component stack trace string into an attachment.
+ *
+ * The stack is appended as a plain string (not wrapped in a `Blob`) so that
+ * React Native's FormData polyfill — which can't serialize browser `Blob`
+ * objects — can upload it successfully. Browsers accept strings on
+ * `FormData.append()` as well, so this works everywhere.
  */
 function createComponentStackAttachment(
   componentStack: string
 ): BugSplatAttachment {
   return {
     filename: 'componentStack.txt',
-    data: new Blob([componentStack]),
+    data: componentStack,
   };
 }