debug(e2e): add logging to diagnose warmServer artifact 404

The local e2e server appears to start (health check passes) but returns
404 for artifact files. Added:
- stdout/stderr capture from bun server subprocess
- spawn error handler
- HTTP response status logging in waitForRequestReady

Author: sunnylqm

Example/e2etest/e2e/globalSetup.ts

@@ -100,12 +100,21 @@ function startServer() {
   const child = spawn('bun', [serverScript], {
     cwd: projectRoot,
     detached: true,
-    stdio: 'ignore',
+    stdio: ['ignore', 'pipe', 'pipe'],
     env: {
       ...process.env,
       E2E_ASSET_PORT: String(LOCAL_UPDATE_PORT),
     },
   });
+  child.stdout?.on('data', (data: Buffer) => {
+    console.log(`[e2e-server] ${data.toString().trim()}`);
+  });
+  child.stderr?.on('data', (data: Buffer) => {
+    console.error(`[e2e-server] ${data.toString().trim()}`);
+  });
+  child.on('error', (err) => {
+    console.error(`[e2e-server] spawn error: ${err}`);
+  });
   child.unref();
   fs.writeFileSync(pidFile, String(child.pid));
 }
@@ -162,8 +171,9 @@ async function waitForRequestReady(
       if (response.ok) {
         return;
       }
-    } catch {
-      // Keep polling until the timeout expires.
+      console.log(`[warmServer] ${label}: status ${response.status}`);
+    } catch (err) {
+      console.log(`[warmServer] ${label}: fetch error: ${err}`);
     }
 
     if (Date.now() - start > timeoutMs) {