Send SMS with Cloudflare Workers

Add SMS sending to this Cloudflare Workers project with TextKit.

- Docs for this stack:
  https://jointextkit.com/docs/send-with-cloudflare-workers.md
- API: POST https://api.jointextkit.com/v1/messages with `Authorization: Bearer
  <key>` and a JSON body `{"to": "+1...", "body": "..."}`.
- Use the official SDK: `npm install jointextkit`, pass the key from the
  Worker's `env` (a secret), then `new
  TextKit(env.TEXTKIT_API_KEY).messages.send({ to, body })`.
- Read the key from the `TEXTKIT_API_KEY` environment variable. Never hardcode
  it or send it to the browser.
- Phone numbers are E.164 and US or Canada only (`+1` followed by 10 digits).
- A test key (`ssms_sk_test_`) simulates: `+15005550006` always ends `delivered`
  and no phone gets a text.
- Errors are JSON: `{"error": {"code", "message", "param"}}` with a 4xx status.
  On `429`, wait `Retry-After` seconds and retry.
- Send only from server code that runs after a real event (a signup, an order).
  Never expose an endpoint that texts any number a visitor types.

export TEXTKIT_API_KEY=ssms_sk_test_...

npm install jointextkit
npx wrangler secret put TEXTKIT_API_KEY

import { TextKit, TextKitError } from 'jointextkit';

interface Env {
  TEXTKIT_API_KEY: string;
}

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    if (request.method !== 'POST') return new Response('Method not allowed', { status: 405 });

    const { to, body } = (await request.json()) as { to: string; body: string };
    const sms = new TextKit(env.TEXTKIT_API_KEY);

    try {
      const message = await sms.messages.send({ to, body });
      return Response.json({ id: message.id, status: message.status });
    } catch (err) {
      if (err instanceof TextKitError) {
        return Response.json({ error: err.code, message: err.message }, { status: err.status });
      }
      throw err;
    }
  },
};

npx wrangler dev

curl -X POST http://localhost:8787 \
  -H "Content-Type: application/json" \
  -d '{"to": "+15005550006", "body": "Hello from TextKit"}'

npx wrangler deploy