fix(langgraph): avoid calling _emit for runs without metadata (#1340)

Author: dqbd

libs/langgraph/src/pregel/messages.test.ts

@@ -321,6 +321,31 @@ describe("StreamMessagesHandler", () => {
       // Should clean up metadata
       expect(handler.metadatas[runId]).toBeUndefined();
     });
+
+    it("should not emit when metadata is missing", () => {
+      const streamFn = vi.fn();
+      const handler = new StreamMessagesHandler(streamFn);
+
+      // Spy on _emit
+      const emitSpy = vi.spyOn(handler, "_emit");
+
+      handler.handleLLMEnd(
+        {
+          generations: [
+            [
+              {
+                text: "test output",
+                message: new AIMessage({ content: "result" }),
+              },
+            ],
+          ],
+        } as unknown as LLMResult,
+        "run-123"
+      );
+
+      // Should not emit anything
+      expect(emitSpy).not.toHaveBeenCalled();
+    });
   });
 
   describe("handleLLMError", () => {

libs/langgraph/src/pregel/messages.ts

@@ -39,7 +39,7 @@ export class StreamMessagesHandler extends BaseCallbackHandler {
 
   streamFn: (streamChunk: StreamChunk) => void;
 
-  metadatas: Record<string, Meta> = {};
+  metadatas: Record<string, Meta | undefined> = {};
 
   seen: Record<string, BaseMessage> = {};
 
@@ -146,6 +146,9 @@ export class StreamMessagesHandler extends BaseCallbackHandler {
   }
 
   handleLLMEnd(output: LLMResult, runId: string) {
+    // Filter out runs that we do not have metadata for
+    if (this.metadatas[runId] === undefined) return;
+
     // In JS, non-streaming runs do not call handleLLMNewToken at the model level
     if (!this.emittedChatModelRunIds[runId]) {
       const chatGeneration = output.generations?.[0]?.[0] as ChatGeneration;