Skip retry for auth errors on ingest endpoint

.changeset/ingest-auth-no-retry.md

@@ -0,0 +1,7 @@
+---
+"@vercel/flags-core": patch
+---
+
+Stop retrying ingest requests on 401/403 auth errors.
+
+Previously the usage tracker would retry up to 3 times on any non-OK response, including authentication failures. Since auth errors are permanent, retrying them wastes requests. The SDK now returns immediately on 401 or 403 without retrying, matching the fast-fail behavior already used by the stream connection.

packages/vercel-flags-core/src/utils/usage-tracker.test.ts

@@ -416,6 +416,42 @@ describe('UsageTracker', () => {
       expect(requestCount).toBe(3);
     });
 
+    it('should not retry on 401 response', async () => {
+      const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+
+      fetchMock.mockResolvedValue(new Response(null, { status: 401 }));
+
+      const tracker = createTracker();
+
+      tracker.trackRead();
+      await tracker.flush();
+
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+      expect(errorSpy).toHaveBeenCalledWith(
+        '@vercel/flags-core: Ingest auth error (401), not retrying',
+      );
+
+      errorSpy.mockRestore();
+    });
+
+    it('should not retry on 403 response', async () => {
+      const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+
+      fetchMock.mockResolvedValue(new Response(null, { status: 403 }));
+
+      const tracker = createTracker();
+
+      tracker.trackRead();
+      await tracker.flush();
+
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+      expect(errorSpy).toHaveBeenCalledWith(
+        '@vercel/flags-core: Ingest auth error (403), not retrying',
+      );
+
+      errorSpy.mockRestore();
+    });
+
     it('should retry on fetch error and succeed', async () => {
       let requestCount = 0;
       fetchMock.mockImplementation(async () => {

packages/vercel-flags-core/src/utils/usage-tracker.ts

@@ -276,6 +276,13 @@ export class UsageTracker {
           break; // Break the loop if the request succeeded
         }
 
+        if (response.status === 401 || response.status === 403) {
+          console.error(
+            `@vercel/flags-core: Ingest auth error (${response.status}), not retrying`,
+          );
+          return;
+        }
+
         throw new Error(
           `Ingest endpoint responded with status ${response.status} for ${eventsToSend.length} events on request ${response.headers.get('x-vercel-id')}.\n` +
             `Response body: ${await response.text().catch(() => null)}`,