feat(gro-194): SMS provider service with Telnyx SDK integration

- Added telnyx npm package
- Created sms.ts with SmsProvider interface
- Implemented TelnyxProvider with sendSms() and validateWebhookSignature()
- Added createSmsProvider() factory function
- Added smsSend() convenience function that skips when SMS_ENABLED=false
- Provider abstraction allows future Twilio or other providers
- E.164 phone validation on send
- Webhook signature verification using HMAC-SHA256

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/package.json

@@ -22,6 +22,7 @@
     "hono": "^4.6.17",
     "node-cron": "^3.0.3",
     "nodemailer": "^6.9.16",
+    "telnyx": "^6.41.0",
     "zod": "^4.3.6"
   },
   "devDependencies": {

apps/api/src/services/sms.ts

@@ -0,0 +1,140 @@
+import { Telnyx } from "telnyx";
+
+export interface SmsProvider {
+  sendSms(to: string, body: string, mediaUrls?: string[]): Promise<{ messageId: string; status: string }>;
+  validateWebhookSignature(req: Request): boolean;
+}
+
+interface TelnyxSmsResult {
+  message_id: string;
+  status: string;
+}
+
+function createTelnyxClient(): Telnyx | null {
+  const apiKey = process.env.TELNYX_API_KEY;
+  if (!apiKey) return null;
+  return new Telnyx(apiKey);
+}
+
+let _client: Telnyx | null | undefined;
+
+function getClient(): Telnyx | null {
+  if (_client === undefined) _client = createTelnyxClient();
+  return _client;
+}
+
+function getFromNumber(): string | null {
+  return process.env.TELNYX_FROM_NUMBER ?? null;
+}
+
+function isE164(phone: string): boolean {
+  return /^\+[1-9]\d{7,14}$/.test(phone);
+}
+
+export async function sendSms(
+  to: string,
+  body: string,
+  mediaUrls?: string[]
+): Promise<{ messageId: string; status: string }> {
+  const client = getClient();
+  if (!client) throw new Error("Telnyx client not initialized. Set TELNYX_API_KEY.");
+
+  const from = getFromNumber();
+  if (!from) throw new Error("TELNYX_FROM_NUMBER is not set");
+
+  if (!isE164(to)) throw new Error(`Invalid recipient phone format: ${to}. Expected E.164.`);
+  if (!isE164(from)) throw new Error(`Invalid sender phone format: ${from}. Expected E.164.`);
+
+  const payload: Record<string, unknown> = {
+    from,
+    to,
+    body,
+  };
+
+  if (mediaUrls && mediaUrls.length > 0) {
+    payload.media_urls = mediaUrls;
+  }
+
+  const result = await client.messages.create(payload as Record<string, string | string[]>);
+  const smsResult = result.data as unknown as TelnyxSmsResult;
+  return {
+    messageId: smsResult.message_id,
+    status: smsResult.status,
+  };
+}
+
+export class TelnyxProvider implements SmsProvider {
+  async sendSms(
+    to: string,
+    body: string,
+    mediaUrls?: string[]
+  ): Promise<{ messageId: string; status: string }> {
+    return sendSms(to, body, mediaUrls);
+  }
+
+  validateWebhookSignature(req: Request): boolean {
+    const secret = process.env.TELNYX_WEBHOOK_SECRET;
+    if (!secret) return false;
+
+    const signature = req.headers.get("telnyx-signature");
+    if (!signature) return false;
+
+    const payload = JSON.stringify(req.body);
+
+    try {
+      const { createHmac } = await import("crypto");
+      const hmac = createHmac("sha256", secret);
+      const expected = `sha256=${hmac.update(payload).digest("hex")}`;
+
+      const sigBuf = Buffer.from(signature);
+      const expBuf = Buffer.from(expected);
+
+      if (sigBuf.length !== expBuf.length) return false;
+
+      let diff = 0;
+      for (let i = 0; i < sigBuf.length; i++) {
+        diff |= sigBuf[i] ^ expBuf[i];
+      }
+      return diff === 0;
+    } catch {
+      return false;
+    }
+  }
+}
+
+let _provider: SmsProvider | null | undefined;
+
+export function createSmsProvider(): SmsProvider | null {
+  if (_provider === undefined) {
+    if (process.env.SMS_ENABLED !== "true") {
+      _provider = null;
+      return null;
+    }
+    switch (process.env.SMS_PROVIDER) {
+      case "telnyx": {
+        const client = getClient();
+        if (!client) {
+          _provider = null;
+          return null;
+        }
+        _provider = new TelnyxProvider();
+        break;
+      }
+      default:
+        _provider = null;
+    }
+  }
+  return _provider;
+}
+
+export async function smsSend(
+  to: string,
+  body: string,
+  mediaUrls?: string[]
+): Promise<boolean> {
+  const provider = createSmsProvider();
+  if (!provider) return false;
+
+  await provider.sendSms(to, body, mediaUrls);
+  return true;
+}