fix: remove auto-flush wiring from SegmentDestination, add CDN validation tests

Remove autoFlushOnRetryReady check, setAutoFlushCallback call, and shutdown()
method. Add tests for CDN integrations validation (null, array, string, and
no-defaults scenarios).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abueide

packages/core/src/__tests__/internal/fetchSettings.test.ts

@@ -436,6 +436,69 @@ describe('internal #getSettings', () => {
     });
   });
 
+  describe('CDN integrations validation', () => {
+    it('falls back to defaults when CDN returns null integrations', async () => {
+      (fetch as jest.MockedFunction<typeof fetch>).mockResolvedValueOnce({
+        ok: true,
+        json: () => Promise.resolve({ integrations: null }),
+        status: 200,
+      } as Response);
+
+      const client = new SegmentClient(clientArgs);
+      await client.fetchSettings();
+
+      expect(setSettingsSpy).toHaveBeenCalledWith(
+        defaultIntegrationSettings.integrations
+      );
+    });
+
+    it('falls back to defaults when CDN returns integrations as an array', async () => {
+      (fetch as jest.MockedFunction<typeof fetch>).mockResolvedValueOnce({
+        ok: true,
+        json: () => Promise.resolve({ integrations: ['invalid'] }),
+        status: 200,
+      } as Response);
+
+      const client = new SegmentClient(clientArgs);
+      await client.fetchSettings();
+
+      expect(setSettingsSpy).toHaveBeenCalledWith(
+        defaultIntegrationSettings.integrations
+      );
+    });
+
+    it('falls back to defaults when CDN returns integrations as a string', async () => {
+      (fetch as jest.MockedFunction<typeof fetch>).mockResolvedValueOnce({
+        ok: true,
+        json: () => Promise.resolve({ integrations: 'invalid' }),
+        status: 200,
+      } as Response);
+
+      const client = new SegmentClient(clientArgs);
+      await client.fetchSettings();
+
+      expect(setSettingsSpy).toHaveBeenCalledWith(
+        defaultIntegrationSettings.integrations
+      );
+    });
+
+    it('does not set settings when CDN returns invalid integrations and no defaults', async () => {
+      (fetch as jest.MockedFunction<typeof fetch>).mockResolvedValueOnce({
+        ok: true,
+        json: () => Promise.resolve({ integrations: null }),
+        status: 200,
+      } as Response);
+
+      const client = new SegmentClient({
+        ...clientArgs,
+        config: { ...clientArgs.config, defaultSettings: undefined },
+      });
+      await client.fetchSettings();
+
+      expect(setSettingsSpy).not.toHaveBeenCalled();
+    });
+  });
+
   describe('httpConfig extraction', () => {
     it('extracts httpConfig from CDN response and merges with defaults', async () => {
       const serverHttpConfig = {

packages/core/src/plugins/SegmentDestination.ts

@@ -369,12 +369,6 @@ export class SegmentDestination extends DestinationPlugin {
           this.analytics?.logger,
           config?.retryStrategy ?? 'lazy'
         );
-
-        if (config?.autoFlushOnRetryReady === true) {
-          this.retryManager.setAutoFlushCallback(() => {
-            void this.flush();
-          });
-        }
       }
     }
 
@@ -390,8 +384,4 @@ export class SegmentDestination extends DestinationPlugin {
     // Wait until the queue is done restoring before flushing
     return this.queuePlugin.flush();
   }
-
-  shutdown(): void {
-    this.retryManager?.destroy();
-  }
 }