feat(langchain/createAgent): Add support for modelSettings to middleware

libs/langchain/src/agents/middlewareAgent/nodes/AgentNode.ts

@@ -290,7 +290,11 @@ export class AgentNode<
     }
 
     const signal = mergeAbortSignals(this.#options.signal, config.signal);
-    const invokeConfig = { ...config, signal };
+    const invokeConfig = {
+      ...config,
+      signal,
+      ...preparedOptions?.callOptions,
+    };
     const response = (await modelWithTools.invoke(
       modelInput,
       invokeConfig

libs/langchain/src/agents/middlewareAgent/tests/callOptions.test.ts

@@ -0,0 +1,284 @@
+import { expect, describe, it, vi, type MockInstance } from "vitest";
+import { HumanMessage, AIMessage } from "@langchain/core/messages";
+import type { LanguageModelLike } from "@langchain/core/language_models/base";
+
+import { createAgent, createMiddleware } from "../index.js";
+
+function createMockModel(name = "ChatAnthropic", model = "anthropic") {
+  // Mock Anthropic model
+  const invokeCallback = vi
+    .fn()
+    .mockResolvedValue(new AIMessage("Response from model"));
+  return {
+    getName: () => name,
+    bindTools: vi.fn().mockReturnThis(),
+    _streamResponseChunks: vi.fn().mockReturnThis(),
+    bind: vi.fn().mockReturnThis(),
+    invoke: invokeCallback,
+    lc_runnable: true,
+    _modelType: model,
+    _generate: vi.fn(),
+    _llmType: () => model,
+  } as unknown as LanguageModelLike;
+}
+
+describe("callOptions middleware support", () => {
+  it("should pass callOptions from middleware to model.invoke", async () => {
+    const model = createMockModel();
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            temperature: 0.5,
+            max_tokens: 100,
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    expect(config).toHaveProperty("temperature", 0.5);
+    expect(config).toHaveProperty("max_tokens", 100);
+  });
+
+  it("should pass headers from middleware callOptions to model.invoke", async () => {
+    const model = createMockModel();
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            headers: {
+              "X-Custom-Header": "middleware-value",
+              "X-Middleware-Only": "middleware-only",
+            },
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    expect(config.headers).toEqual({
+      "X-Custom-Header": "middleware-value",
+      "X-Middleware-Only": "middleware-only",
+    });
+  });
+
+  it("should pass headers from middleware callOptions to model.invoke config", async () => {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const model = createMockModel() as any;
+
+    // Middleware that adds headers via callOptions
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            headers: {
+              "X-Middleware-Header": "from-middleware",
+              "X-Custom-Header": "custom-value",
+            },
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    // Verify model.invoke was called with headers in the config
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+
+    expect(config.headers).toEqual({
+      "X-Middleware-Header": "from-middleware",
+      "X-Custom-Header": "custom-value",
+    });
+  });
+
+  it("should handle callOptions without headers", async () => {
+    const model = createMockModel();
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            temperature: 0.7,
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    expect(config).toHaveProperty("temperature", 0.7);
+    expect(config.headers).toBeUndefined();
+  });
+
+  it("should only add headers when either config or callOptions has headers", async () => {
+    const model = createMockModel();
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            temperature: 0.8,
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    expect(config).not.toHaveProperty("headers");
+  });
+
+  it("should support multiple middleware with callOptions", async () => {
+    const model = createMockModel();
+    const middleware1 = createMiddleware({
+      name: "middleware1",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            temperature: 0.5,
+            headers: {
+              "X-Middleware-1": "value1",
+            },
+          },
+        };
+      },
+    });
+
+    const middleware2 = createMiddleware({
+      name: "middleware2",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            max_tokens: 200,
+            headers: {
+              "X-Middleware-2": "value2",
+            },
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware1, middleware2] as const,
+    });
+
+    await agent.invoke({
+      messages: [new HumanMessage("Hello, world!")],
+    });
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    // Last middleware wins for overlapping properties
+    expect(config).toHaveProperty("max_tokens", 200);
+    expect(config.headers).toEqual({
+      "X-Middleware-2": "value2",
+    });
+  });
+
+  it("should preserve signal from config when merging callOptions", async () => {
+    const model = createMockModel();
+    const abortController = new AbortController();
+    const middleware = createMiddleware({
+      name: "testMiddleware",
+      modifyModelRequest: async (request) => {
+        return {
+          ...request,
+          callOptions: {
+            temperature: 0.5,
+          },
+        };
+      },
+    });
+
+    const agent = createAgent({
+      model,
+      tools: [],
+      middleware: [middleware] as const,
+    });
+
+    await agent.invoke(
+      {
+        messages: [new HumanMessage("Hello, world!")],
+      },
+      {
+        signal: abortController.signal,
+      }
+    );
+
+    expect(model.invoke).toHaveBeenCalled();
+    const callArgs = (model.invoke as unknown as MockInstance).mock.calls[0];
+    const config = callArgs[1];
+    expect(config).toHaveProperty("signal");
+    expect(config).toHaveProperty("temperature", 0.5);
+  });
+});

libs/langchain/src/agents/middlewareAgent/types.ts

@@ -152,6 +152,11 @@ export interface ModelRequest {
    * The tools to make available for this step.
    */
   tools: string[];
+
+  /**
+   * Extra call options to pass to the model.
+   */
+  callOptions?: Record<string, unknown>;
 }
 
 /**