fix(core): Fix interop case where callbacks are manually passed to a runnable, t… (#8696)

Author: jacoblee93

docs/core_docs/docusaurus.config.js

@@ -146,7 +146,8 @@ const config = {
         respectPrefersColorScheme: true,
       },
       announcementBar: {
-        content: 'Our new LangChain Academy Course Deep Research with LangGraph is now live! <a href="https://academy.langchain.com/courses/deep-research-with-langgraph/?utm_medium=internal&utm_source=docs&utm_campaign=q3-2025_deep-research-course_co" target="_blank">Enroll for free</a>.',
+        content:
+          'Our new LangChain Academy Course Deep Research with LangGraph is now live! <a href="https://academy.langchain.com/courses/deep-research-with-langgraph/?utm_medium=internal&utm_source=docs&utm_campaign=q3-2025_deep-research-course_co" target="_blank">Enroll for free</a>.',
         backgroundColor: "#d0c9fe",
       },
       prism: {

langchain-core/src/tracers/tests/langsmith_interop.int.test.ts

@@ -4,6 +4,7 @@ import { traceable } from "langsmith/traceable";
 import { RunnableLambda } from "../../runnables/base.js";
 import { BaseMessage, HumanMessage } from "../../messages/index.js";
 import { awaitAllCallbacks } from "../../singletons/callbacks.js";
+import { LangChainTracer } from "../tracer_langchain.js";
 
 test("traceables double nested within runnables with batching", async () => {
   const aiGreet = traceable(
@@ -27,3 +28,28 @@ test("traceables double nested within runnables with batching", async () => {
 
   await awaitAllCallbacks();
 });
+
+test("runnable nested within a traceable with manual tracer passed", async () => {
+  const aiGreet = traceable(
+    async (msg: BaseMessage) => {
+      const child = RunnableLambda.from(async () => {
+        return [new HumanMessage({ content: "From child!" })];
+      }).withConfig({ runName: "child" });
+      return child.invoke([msg]);
+    },
+    { name: "aiGreet", tracingEnabled: true }
+  );
+
+  const parent = RunnableLambda.from(async () => {
+    return aiGreet(new HumanMessage({ content: "Hello!" }));
+  }).withConfig({ runName: "parent" });
+
+  await parent.invoke(
+    {},
+    {
+      callbacks: [new LangChainTracer()],
+    }
+  );
+
+  await awaitAllCallbacks();
+});

langchain-core/src/tracers/tracer_langchain.ts

@@ -91,6 +91,7 @@ export class LangChainTracer
   }
 
   updateFromRunTree(runTree: RunTree) {
+    this.runTreeMap.set(runTree.id, runTree);
     let rootRun: RunTree = runTree;
     const visited = new Set<string>();
     while (rootRun.parent_run) {