fix(core): route replay events in multiplexed transport

Co-Authored-By: GPT-5 <noreply@anthropic.com>

Author: logaretm

packages/core/src/transports/multiplexed.ts

@@ -102,7 +102,7 @@ export function makeMultiplexedTransport<TO extends BaseTransportOptions>(
     const actualMatcher: Matcher =
       matcher ||
       (args => {
-        const event = args.getEvent();
+        const event = args.getEvent(['event', 'replay_event']);
         if (
           event?.extra?.[MULTIPLEXED_TRANSPORT_EXTRA_KEY] &&
           Array.isArray(event.extra[MULTIPLEXED_TRANSPORT_EXTRA_KEY])

packages/core/test/lib/transports/multiplexed.test.ts

@@ -30,6 +30,7 @@ const TRANSACTION_ENVELOPE = createEnvelope<EventEnvelope>(
   { event_id: 'aa3ff046696b4bc6b609ce6d28fde9e2', sent_at: '123' },
   [[{ type: 'transaction' }, TRANSACTION_EVENT] as EventItem],
 );
+const REPLAY_EVENT = { type: 'replay_event', event_id: 'aa3ff046696b4bc6b609ce6d28fde9e2' };
 
 const DEFAULT_DISCARDED_EVENTS: ClientReport['discarded_events'] = [
   {
@@ -320,4 +321,34 @@ describe('makeMultiplexedTransport() with default matcher', () => {
     const transport = makeTransport({ url: DSN1_URL, ...transportOptions });
     await transport.send(envelope);
   });
+
+  it('sends replay events to targets provided in event.extra[MULTIPLEXED_TRANSPORT_EXTRA_KEY]', async () => {
+    expect.assertions(2);
+
+    const makeTransport = makeMultiplexedTransport(
+      createTestTransport(
+        url => {
+          expect(url).toBe(DSN1_URL);
+        },
+        url => {
+          expect(url).toBe(DSN2_URL);
+        },
+      ),
+    );
+
+    const envelope = createEnvelope<EventEnvelope>({ event_id: 'aa3ff046696b4bc6b609ce6d28fde9e2', sent_at: '123' }, [
+      [
+        { type: 'replay_event' },
+        {
+          ...REPLAY_EVENT,
+          extra: {
+            [MULTIPLEXED_TRANSPORT_EXTRA_KEY]: [DSN1, DSN2],
+          },
+        },
+      ] as EventItem,
+    ]);
+
+    const transport = makeTransport({ url: DSN1_URL, ...transportOptions });
+    await transport.send(envelope);
+  });
 });