🧵 fix: Prevent Message Loading Race During Streaming (#13295)

packages/api/src/stream/__tests__/RedisEventTransport.spec.ts

@@ -0,0 +1,56 @@
+import type { Redis } from 'ioredis';
+import { logger } from '@librechat/data-schemas';
+import { RedisEventTransport } from '~/stream/implementations/RedisEventTransport';
+import { createMockPublisher } from './helpers/publisher';
+
+logger.silent = true;
+
+function createMockSubscriber() {
+  return {
+    on: jest.fn(),
+    subscribe: jest.fn().mockResolvedValue(undefined),
+    unsubscribe: jest.fn().mockResolvedValue(undefined),
+  };
+}
+
+function getMessageHandler(mockSubscriber: ReturnType<typeof createMockSubscriber>) {
+  return mockSubscriber.on.mock.calls.find((call) => call[0] === 'message')?.[1] as (
+    channel: string,
+    message: string,
+  ) => void;
+}
+
+describe('RedisEventTransport', () => {
+  it('resets stale abort-listener reorder state before the next real subscriber', async () => {
+    const mockPublisher = createMockPublisher();
+    const mockSubscriber = createMockSubscriber();
+    const transport = new RedisEventTransport(
+      mockPublisher as unknown as Redis,
+      mockSubscriber as unknown as Redis,
+    );
+
+    const streamId = 'reorder-abort-listener-reuse-test';
+    transport.onAbort(streamId, () => {});
+
+    const messageHandler = getMessageHandler(mockSubscriber);
+    const channel = `stream:{${streamId}}:events`;
+
+    for (let i = 0; i < 5; i++) {
+      await transport.emitChunk(streamId, { index: i });
+      messageHandler(channel, JSON.stringify({ type: 'chunk', seq: i, data: { index: i } }));
+    }
+
+    await mockPublisher.del(`stream:{${streamId}}:seq`);
+
+    const secondRunChunks: unknown[] = [];
+    transport.subscribe(streamId, {
+      onChunk: (event) => secondRunChunks.push(event),
+    });
+
+    messageHandler(channel, JSON.stringify({ type: 'chunk', seq: 0, data: { index: 0 } }));
+
+    expect(secondRunChunks.map((chunk) => (chunk as { index: number }).index)).toEqual([0]);
+
+    transport.destroy();
+  });
+});

packages/api/src/stream/implementations/RedisEventTransport.ts

@@ -439,6 +439,12 @@ export class RedisEventTransport implements IEventTransport {
     }
 
     const streamState = this.streams.get(streamId)!;
+    // Internal listeners (for example cross-replica abort) can leave ordering
+    // state behind with no real SSE subscribers. A new subscriber is a fresh
+    // attachment and must not inherit that prior generation's expected seq.
+    if (streamState.count === 0) {
+      this.resetReorderBuffer(streamId);
+    }
     streamState.count++;
     streamState.handlers.set(subscriberId, handlers);