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fix(langchain): preserve custom ChatMessage role instead of hardcoding "human" #833

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fix(langchain): preserve custom ChatMessage role instead of hardcoding "human" #833

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4 changes: 3 additions & 1 deletion packages/langchain/src/CallbackHandler.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -931,7 +931,9 @@ export class CallbackHandler extends BaseCallbackHandler {
} else if (message.getType() === "generic") {
response = {
content: message.content,
role: "human",
// ChatMessage (getType() === "generic") carries a custom role; preserve
// it instead of hardcoding "human" (regression introduced in #680).
role: (message as any).role ?? "human",
};
} else if (message.getType() === "ai") {
response = { content: message.content, role: "assistant" };
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11 changes: 11 additions & 0 deletions tests/integration/langchain.integration.test.ts
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import { ChatMessage } from "@langchain/core/messages";
import { DynamicTool } from "@langchain/core/tools";
import { CallbackHandler } from "@langfuse/langchain";
import { LangfuseOtelSpanAttributes } from "@langfuse/tracing";
Expand All @@ -24,6 +25,16 @@ describe("LangChain callback handler integration tests", () => {
await teardownTestEnvironment(testEnv);
});

it("should preserve custom roles for ChatMessage (generic) inputs", () => {
const handler = new CallbackHandler();

const mapped = (handler as any).extractChatMessageContent(
new ChatMessage({ content: "hello", role: "developer" }),
);

expect(mapped).toEqual({ content: "hello", role: "developer" });
});

it("should mark LangChain tool runs as tool observations", async () => {
const calculatorTool = new DynamicTool({
name: "calculator",
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