Fix envelope header parsing

functions/api/st.ts

@@ -1,13 +1,19 @@
 import { jsonError } from "../common.js";
 
 export async function onRequestPost(context: RequestContext) {
-  const dsn = context.request.headers.get("dsn");
+  const clonedRequest = context.request.clone();
+  const header = (await context.request.text()).split("\n").at(0);
 
-  if (!dsn || dsn !== context.env.DSN) return jsonError("Bad or no DSN", 400);
+  if (!header) return jsonError("Failed to parse envelope header", 500);
+
+  const { dsn } = JSON.parse(header);
+
+  if (context.env.DSN !== dsn) return jsonError("Bad or no DSN", 400);
 
   const sentryUrl = new URL(dsn);
+
   await fetch(`https://${sentryUrl.host}/api${sentryUrl.pathname}/envelope`, {
-    body: context.request.body,
+    body: clonedRequest.body,
     headers: {
       "content-type": "application/x-sentry-envelope",
       "x-forwarded-for": context.request.headers.get(