fix(@langchain/google-genai): support custom agent names in createAgent (#9583)

Co-authored-by: Hunter Lovell <[email protected]>
Co-authored-by: Hunter Lovell <[email protected]>

Author: maslo55555

.changeset/great-dingos-exist.md

@@ -0,0 +1,5 @@
+---
+"@langchain/google-genai": patch
+---
+
+fix(google-genai): support custom agent names in createAgent

libs/providers/langchain-google-genai/src/tests/chat_models.test.ts

@@ -15,6 +15,7 @@ import { removeAdditionalProperties } from "../utils/zod_to_genai_parameters.js"
 import {
   convertBaseMessagesToContent,
   convertMessageContentToParts,
+  getMessageAuthor,
 } from "../utils/common.js";
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -962,3 +963,43 @@ test("convertMessageContentToParts: correctly handles ToolMessage with array con
     },
   ]);
 });
+
+test("getMessageAuthor should return message type, not custom names", () => {
+  const aiMessageWithName = new AIMessage({
+    content: "Hello",
+    name: "math_expert",
+  });
+  expect(getMessageAuthor(aiMessageWithName)).toBe("ai");
+
+  const aiMessage = new AIMessage({
+    content: "Hello",
+  });
+  expect(getMessageAuthor(aiMessage)).toBe("ai");
+
+  const humanMessage = new HumanMessage({
+    content: "Hello",
+  });
+  expect(getMessageAuthor(humanMessage)).toBe("human");
+
+  const toolMessage = new ToolMessage({
+    content: "Result",
+    tool_call_id: "123",
+  });
+  expect(getMessageAuthor(toolMessage)).toBe("tool");
+});
+
+test("convertBaseMessagesToContent should handle AIMessages with custom names", () => {
+  const messages = [
+    new HumanMessage({ content: "What is 2+2?" }),
+    new AIMessage({ content: "4", name: "math_expert" }),
+  ];
+
+  expect(() =>
+    convertBaseMessagesToContent(messages, true, false, "model")
+  ).not.toThrow();
+
+  const result = convertBaseMessagesToContent(messages, true, false, "model");
+  expect(result).toHaveLength(2);
+  expect(result[0].role).toBe("user");
+  expect(result[1].role).toBe("model");
+});

libs/providers/langchain-google-genai/src/utils/common.ts

@@ -53,14 +53,10 @@ const DUMMY_SIGNATURE =
 const iife = (fn: () => string) => fn();
 
 export function getMessageAuthor(message: BaseMessage) {
-  const type = message._getType();
   if (ChatMessage.isInstance(message)) {
     return message.role;
   }
-  if (type === "tool") {
-    return type;
-  }
-  return message.name ?? type;
+  return message.type;
 }
 
 /**
@@ -79,7 +75,7 @@ export function convertAuthorToRole(
      * */
     case "supervisor":
     case "ai":
-    case "model": // getMessageAuthor returns message.name. code ex.: return message.name ?? type;
+    case "model":
       return "model";
     case "system":
       return "system";