fix architecture and write new tests

apps/api/src/http/webhooks.ts

@@ -0,0 +1,18 @@
+import type { Request } from 'express'
+import { ValidationError } from './errors'
+
+export function getRawBodyString(req: Request) {
+  if (!Buffer.isBuffer(req.body)) {
+    throw new ValidationError('Webhook route must be mounted with express.raw before JSON parsing')
+  }
+  return req.body.toString('utf8')
+}
+
+export function parseRawJsonBody<T = unknown>(req: Request): T {
+  const rawBody = getRawBodyString(req)
+  try {
+    return JSON.parse(rawBody) as T
+  } catch {
+    throw new ValidationError('Malformed webhook JSON')
+  }
+}