feat(core): integrate TAPI backoff v2 into upload flow (3/3)

packages/core/src/api.ts

@@ -4,21 +4,28 @@ export const uploadEvents = async ({
   writeKey,
   url,
   events,
+  retryCount = 0,
 }: {
   writeKey: string;
   url: string;
   events: SegmentEvent[];
-}) => {
+  retryCount?: number;
+}): Promise<Response> => {
+  // Create Authorization header (Basic auth format)
+  const authHeader = 'Basic ' + btoa(writeKey + ':');
+
   return await fetch(url, {
     method: 'POST',
     keepalive: true,
     body: JSON.stringify({
       batch: events,
       sentAt: new Date().toISOString(),
-      writeKey: writeKey,
+      writeKey: writeKey, // Keep in body for backwards compatibility
     }),
     headers: {
       'Content-Type': 'application/json; charset=utf-8',
+      'Authorization': authHeader,
+      'X-Retry-Count': retryCount.toString(),
     },
   });
 };

packages/core/src/errors.ts

@@ -99,18 +99,14 @@ export const checkResponseForErrors = (response: Response) => {
  * @returns a SegmentError object
  */
 export const translateHTTPError = (error: unknown): SegmentError => {
-  // SegmentError already
   if (error instanceof SegmentError) {
     return error;
-    // JSON Deserialization Errors
   } else if (error instanceof SyntaxError) {
     return new JSONError(
       ErrorType.JsonUnableToDeserialize,
       error.message,
       error
     );
-
-    // HTTP Errors
   } else {
     const message =
       error instanceof Error