Cada respuesta, en cada canal,
en un solo webhook.

curl https://api.unlimitedmessaging.app/webhooks \
  -H "Authorization: Bearer $UM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "url": "https://example.com/webhooks/um",
    "eventTypes": ["message.received", "message.status", "account.status_changed"],
    "description": "Every reply, every channel"
  }'

# No accountIds: the endpoint covers every WhatsApp number, mailbox and SIM you have,
# including ones linked later. The response carries "secret": "whsec_..." once.

// app/api/webhooks/um/route.ts (Next.js App Router)
import crypto from 'node:crypto';
import { UnlimitedMessagingApiClient } from '@unlimited-messaging/sdk';

const um = new UnlimitedMessagingApiClient({ token: process.env.UM_API_KEY! });
const key = Buffer.from(process.env.UM_WEBHOOK_SECRET!.replace(/^whsec_/, ''), 'base64');

// Standard Webhooks: HMAC-SHA256 of "id.timestamp.rawBody", base64.
function verify(raw: string, id: string, ts: string, header: string) {
  if (Math.abs(Date.now() / 1000 - Number(ts)) > 300) return false;
  const expected = crypto.createHmac('sha256', key).update(`${id}.${ts}.${raw}`).digest('base64');
  return header.split(' ').some((entry) => {
    const sig = entry.startsWith('v1,') ? entry.slice(3) : '';
    return sig.length === expected.length &&
      crypto.timingSafeEqual(Buffer.from(sig), Buffer.from(expected));
  });
}

export async function POST(req: Request) {
  const raw = await req.text();
  const h = req.headers;
  if (!verify(raw, h.get('webhook-id') ?? '', h.get('webhook-timestamp') ?? '',
    h.get('webhook-signature') ?? '')) {
    return new Response('bad signature', { status: 401 });
  }

  const event = JSON.parse(raw);
  if (event.type !== 'message.received') return new Response(null, { status: 200 });

  const { message: m, channel } = event.data;
  // One inbox row, whatever the channel (upsert on eventId: delivery is at least once).
  await inbox.upsert({
    eventId: event.eventId,
    channel: channel.type,                       // WHATSAPP | EMAIL | SMS
    from: m.sender ?? m.senderId,                // +E164 or email address
    thread: channel.conversation.id ?? m.sender, // SMS has no conversation id
    subject: m.subject ?? null,
    text: m.content,
    at: m.sentAt,                                // order on this, not on arrival
  });

  const answer = await draftReply(m.content);    // your LLM call, or null for a human
  if (answer) {
    if (channel.type === 'SMS') {
      await um.messages.messageSend({
        to: { phone: m.sender },
        channels: [{ channel: 'SMS', accountId: channel.account.id }],
        text: answer,
      });
    } else {
      // WhatsApp and email: same chat or same thread, same number or mailbox.
      await um.messages.messageSend({ replyToMessageId: m.id, text: answer });
    }
  }
  return new Response(null, { status: 200 }); // within 10 s; queue slow work
}