fix(core): Fix nested stream events behavior (#6836)

Author: jacoblee93

langchain-core/src/runnables/base.ts

@@ -695,7 +695,7 @@ export abstract class Runnable<
       config.callbacks = callbacks.concat([logStreamCallbackHandler]);
     } else {
       const copiedCallbacks = callbacks.copy();
-      copiedCallbacks.inheritableHandlers.push(logStreamCallbackHandler);
+      copiedCallbacks.addHandler(logStreamCallbackHandler, true);
       // eslint-disable-next-line no-param-reassign
       config.callbacks = copiedCallbacks;
     }
@@ -896,7 +896,7 @@ export abstract class Runnable<
       config.callbacks = callbacks.concat(eventStreamer);
     } else {
       const copiedCallbacks = callbacks.copy();
-      copiedCallbacks.inheritableHandlers.push(eventStreamer);
+      copiedCallbacks.addHandler(eventStreamer, true);
       // eslint-disable-next-line no-param-reassign
       config.callbacks = copiedCallbacks;
     }

langchain-core/src/runnables/tests/runnable_stream_events_v2.test.ts

@@ -4,6 +4,7 @@
 
 import { test, expect, afterEach } from "@jest/globals";
 import { z } from "zod";
+import { AsyncLocalStorage } from "node:async_hooks";
 import {
   RunnableLambda,
   RunnableMap,
@@ -28,8 +29,9 @@ import { DynamicStructuredTool, DynamicTool, tool } from "../../tools/index.js";
 import { Document } from "../../documents/document.js";
 import { PromptTemplate } from "../../prompts/prompt.js";
 import { GenerationChunk } from "../../outputs.js";
-// Import from web to avoid side-effects from AsyncLocalStorage
+// Import from web to avoid top-level side-effects from AsyncLocalStorage
 import { dispatchCustomEvent } from "../../callbacks/dispatch/web.js";
+import { AsyncLocalStorageProviderSingleton } from "../../singletons/index.js";
 
 function reverse(s: string) {
   // Reverse a string.
@@ -138,6 +140,73 @@ test("Runnable streamEvents method on a chat model", async () => {
   ]);
 });
 
+test("Runnable streamEvents call nested in another runnable + passed callbacks should still work", async () => {
+  AsyncLocalStorageProviderSingleton.initializeGlobalInstance(
+    new AsyncLocalStorage()
+  );
+
+  const model = new FakeListChatModel({
+    responses: ["abc"],
+  });
+
+  const events: any[] = [];
+  const container = RunnableLambda.from(async (_) => {
+    const eventStream = model.streamEvents("hello", { version: "v2" });
+    for await (const event of eventStream) {
+      events.push(event);
+    }
+    return events;
+  });
+
+  await container.invoke({}, { callbacks: [{ handleLLMStart: () => {} }] });
+
+  // used here to avoid casting every ID
+  const anyString = expect.any(String) as unknown as string;
+
+  expect(events).toMatchObject([
+    {
+      data: { input: "hello" },
+      event: "on_chat_model_start",
+      name: "FakeListChatModel",
+      metadata: expect.any(Object),
+      run_id: expect.any(String),
+      tags: [],
+    },
+    {
+      data: { chunk: new AIMessageChunk({ id: anyString, content: "a" }) },
+      event: "on_chat_model_stream",
+      name: "FakeListChatModel",
+      metadata: expect.any(Object),
+      run_id: expect.any(String),
+      tags: [],
+    },
+    {
+      data: { chunk: new AIMessageChunk({ id: anyString, content: "b" }) },
+      event: "on_chat_model_stream",
+      name: "FakeListChatModel",
+      metadata: expect.any(Object),
+      run_id: expect.any(String),
+      tags: [],
+    },
+    {
+      data: { chunk: new AIMessageChunk({ id: anyString, content: "c" }) },
+      event: "on_chat_model_stream",
+      name: "FakeListChatModel",
+      metadata: expect.any(Object),
+      run_id: expect.any(String),
+      tags: [],
+    },
+    {
+      data: { output: new AIMessageChunk({ id: anyString, content: "abc" }) },
+      event: "on_chat_model_end",
+      name: "FakeListChatModel",
+      metadata: expect.any(Object),
+      run_id: expect.any(String),
+      tags: [],
+    },
+  ]);
+});
+
 test("Runnable streamEvents method with three runnables", async () => {
   const r = RunnableLambda.from(reverse);
 

langchain-core/src/tracers/event_stream.ts

@@ -364,7 +364,7 @@ export class EventStreamCallbackHandler extends BaseTracer {
       throw new Error(`onLLMNewToken: Run ID ${run.id} not found in run map.`);
     }
     // Top-level streaming events are covered by tapOutputIterable
-    if (run.parent_run_id === undefined) {
+    if (this.runInfoMap.size === 1) {
       return;
     }
     if (runInfo.runType === "chat_model") {