Probe a real outbound fetch alongside the local probes (#1673)

Cache and timer probes come back in single-digit ms while the same
requests take 4-6s wall, so local I/O is not the cost. Neither probe
leaves the isolate. Time a real outbound subrequest, the class the docs
proxy implicates (0.098s direct vs 3-6s through the Worker).

Author: RhysSullivan

apps/cloud/src/server.ts

@@ -210,13 +210,28 @@ const cloudflareHandler: ExportedHandler<Env> = {
     await scheduler.wait(1);
     const timerProbeMs = Date.now() - timerStartedAt;
 
+    // The cache and timer probes are LOCAL. Neither leaves the isolate, and
+    // both come back in single-digit ms while the same requests take 4-6s.
+    // This one is a real outbound network subrequest to a small, fast,
+    // unrelated endpoint — the only class of I/O not yet measured, and the
+    // one the docs proxy (0.098s direct, 3-6s through the Worker) implicates.
+    const fetchStartedAt = Date.now();
+    // oxlint-disable-next-line executor/no-try-catch-or-throw -- temporary diagnostic: a probe failure must not affect the request
+    try {
+      await fetch("https://cloudflare.com/cdn-cgi/trace", { method: "GET" });
+    } catch {
+      // ignored — the timing is the signal, not the result
+    }
+    const fetchProbeMs = Date.now() - fetchStartedAt;
+
     console.log(
       JSON.stringify({
         probe: "clock-sync",
         path: probeUrl.pathname,
         preWorkMs,
         cacheProbeMs,
         timerProbeMs,
+        fetchProbeMs,
       }),
     );