fix: check Lambda execution errors in S3 uploader

The upload function now properly checks the result of lambda.send() and throws an exception when the Lambda execution fails. This ensures that errors from the batch processor are properly propagated up the call stack.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: snoble

packages/sst/support/custom-resources/s3-uploader.ts

@@ -77,7 +77,7 @@ async function uploadFiles(props: Props) {
     fileOptions,
     replaceValues,
   } = props;
-  await Promise.all(
+  const results = await Promise.all(
     sources.map((source) =>
       lambda.send(
         new InvokeCommand({
@@ -96,6 +96,14 @@ async function uploadFiles(props: Props) {
       )
     )
   );
+
+  // Check for Lambda execution errors
+  results.forEach((result) => {
+    if (result.FunctionError) {
+      const payload = result.Payload ? new TextDecoder().decode(result.Payload) : 'Unknown error';
+      throw new Error(`Lambda execution failed: ${result.FunctionError}. Details: ${payload}`);
+    }
+  });
 }
 
 async function purgeOldFiles(props: Props) {