feat: add send_email MCP tool

lib/const.ts

@@ -19,3 +19,6 @@ export const INBOUND_EMAIL_DOMAIN = "@mail.recoupable.com";
 export const OUTBOUND_EMAIL_DOMAIN = "@recoupable.com";
 
 export const SUPABASE_STORAGE_BUCKET = "user-files";
+
+/** Default from address for outbound emails sent by the agent */
+export const RECOUP_FROM_EMAIL = `Agent by Recoup <agent${OUTBOUND_EMAIL_DOMAIN}>`;

lib/emails/sendEmailSchema.ts

@@ -0,0 +1,29 @@
+import { z } from "zod";
+
+export const sendEmailSchema = z.object({
+  to: z.array(z.string()).describe("Recipient email address or array of addresses"),
+  cc: z
+    .array(z.string())
+    .describe(
+      "Optional array of CC email addresses. active_account_email should always be included unless already in 'to'.",
+    )
+    .default([])
+    .optional(),
+  subject: z.string().describe("Email subject line"),
+  text: z
+    .string()
+    .describe("Plain text body of the email. Use context to make this creative and engaging.")
+    .optional(),
+  html: z
+    .string()
+    .describe("HTML body of the email. Use context to make this creative and engaging.")
+    .default("")
+    .optional(),
+  headers: z
+    .record(z.string(), z.string())
+    .describe("Optional custom headers for the email")
+    .default({})
+    .optional(),
+});
+
+export type SendEmailInput = z.infer<typeof sendEmailSchema>;

lib/mcp/tools/__tests__/registerSendEmailTool.test.ts

@@ -0,0 +1,101 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { registerSendEmailTool } from "../registerSendEmailTool";
+import { NextResponse } from "next/server";
+
+const mockSendEmailWithResend = vi.fn();
+
+vi.mock("@/lib/emails/sendEmail", () => ({
+  sendEmailWithResend: (...args: unknown[]) => mockSendEmailWithResend(...args),
+}));
+
+describe("registerSendEmailTool", () => {
+  let mockServer: McpServer;
+  let registeredHandler: (args: unknown) => Promise<unknown>;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+
+    mockServer = {
+      registerTool: vi.fn((name, config, handler) => {
+        registeredHandler = handler;
+      }),
+    } as unknown as McpServer;
+
+    registerSendEmailTool(mockServer);
+  });
+
+  it("registers the send_email tool", () => {
+    expect(mockServer.registerTool).toHaveBeenCalledWith(
+      "send_email",
+      expect.objectContaining({
+        description: expect.stringContaining("Send an email using the Resend API"),
+      }),
+      expect.any(Function),
+    );
+  });
+
+  it("returns success when email is sent successfully", async () => {
+    mockSendEmailWithResend.mockResolvedValue({ id: "email-123" });
+
+    const result = await registeredHandler({
+      to: ["[email protected]"],
+      subject: "Test Subject",
+      text: "Test body",
+    });
+
+    expect(mockSendEmailWithResend).toHaveBeenCalledWith({
+      from: "Agent by Recoup <[email protected]>",
+      to: ["[email protected]"],
+      cc: undefined,
+      subject: "Test Subject",
+      text: "Test body",
+      html: undefined,
+      headers: {},
+    });
+
+    expect(result).toEqual({
+      content: [
+        {
+          type: "text",
+          text: expect.stringContaining("Email sent successfully"),
+        },
+      ],
+    });
+  });
+
+  it("includes CC addresses when provided", async () => {
+    mockSendEmailWithResend.mockResolvedValue({ id: "email-123" });
+
+    await registeredHandler({
+      to: ["[email protected]"],
+      cc: ["[email protected]"],
+      subject: "Test Subject",
+    });
+
+    expect(mockSendEmailWithResend).toHaveBeenCalledWith(
+      expect.objectContaining({
+        cc: ["[email protected]"],
+      }),
+    );
+  });
+
+  it("returns error when sendEmailWithResend returns NextResponse", async () => {
+    const errorResponse = NextResponse.json({ error: { message: "Rate limited" } }, { status: 429 });
+    mockSendEmailWithResend.mockResolvedValue(errorResponse);
+
+    const result = await registeredHandler({
+      to: ["[email protected]"],
+      subject: "Test Subject",
+    });
+
+    expect(result).toEqual({
+      content: [
+        {
+          type: "text",
+          text: expect.stringContaining("Rate limited"),
+        },
+      ],
+    });
+  });
+});

lib/mcp/tools/index.ts

@@ -13,6 +13,7 @@ import { registerAllFileTools } from "./files";
 import { registerCreateSegmentsTool } from "./registerCreateSegmentsTool";
 import { registerAllYouTubeTools } from "./youtube";
 import { registerTranscribeTools } from "./transcribe";
+import { registerSendEmailTool } from "./registerSendEmailTool";
 
 /**
  * Registers all MCP tools on the server.
@@ -35,4 +36,5 @@ export const registerAllTools = (server: McpServer): void => {
   registerUpdateAccountInfoTool(server);
   registerCreateSegmentsTool(server);
   registerAllYouTubeTools(server);
+  registerSendEmailTool(server);
 };

lib/mcp/tools/registerSendEmailTool.ts

@@ -0,0 +1,49 @@
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { sendEmailSchema, type SendEmailInput } from "@/lib/emails/sendEmailSchema";
+import { sendEmailWithResend } from "@/lib/emails/sendEmail";
+import { getToolResultSuccess } from "@/lib/mcp/getToolResultSuccess";
+import { getToolResultError } from "@/lib/mcp/getToolResultError";
+import { RECOUP_FROM_EMAIL } from "@/lib/const";
+import { NextResponse } from "next/server";
+
+/**
+ * Registers the "send_email" tool on the MCP server.
+ * Send an email using the Resend API.
+ *
+ * @param server - The MCP server instance to register the tool on.
+ */
+export function registerSendEmailTool(server: McpServer): void {
+  server.registerTool(
+    "send_email",
+    {
+      description: `Send an email using the Resend API. Requires 'to' and 'subject'. Optionally include 'text', 'html', and custom headers.\n\nNotes:\n- Emails are sent from ${RECOUP_FROM_EMAIL}.\n- Use context to make the email creative and engaging.\n- Use this tool to send transactional or notification emails to users or admins.`,
+      inputSchema: sendEmailSchema,
+    },
+    async (args: SendEmailInput) => {
+      const { to, cc = [], subject, text, html = "", headers = {} } = args;
+
+      const result = await sendEmailWithResend({
+        from: RECOUP_FROM_EMAIL,
+        to,
+        cc: cc.length > 0 ? cc : undefined,
+        subject,
+        text,
+        html: html || undefined,
+        headers,
+      });
+
+      if (result instanceof NextResponse) {
+        const data = await result.json();
+        return getToolResultError(
+          data?.error?.message || `Failed to send email from ${RECOUP_FROM_EMAIL} to ${to}.`,
+        );
+      }
+
+      return getToolResultSuccess({
+        success: true,
+        message: `Email sent successfully from ${RECOUP_FROM_EMAIL} to ${to}. CC: ${cc.length > 0 ? JSON.stringify(cc) : "none"}.`,
+        data: result,
+      });
+    },
+  );
+}