fix: resolve server entry filename from bundle chunks (#3719)

Closes #3655

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bartlomieju

packages/plugin-vite/src/plugins/server_entry.ts

@@ -103,6 +103,16 @@ if (import.meta.hot) import.meta.hot.accept();`;
       },
     },
     async writeBundle(_options, bundle) {
+      // Find server entry filename directly from bundle chunks.
+      // This is more reliable than the manifest when rollupOptions
+      // override output.entryFileNames.
+      for (const chunk of Object.values(bundle)) {
+        if (chunk.type === "chunk" && chunk.isEntry) {
+          serverEntryFilename = chunk.fileName;
+          break;
+        }
+      }
+
       const manifest = bundle[".vite/manifest.json"];
 
       const staticFiles: PendingStaticFile[] = [];
@@ -113,10 +123,6 @@ if (import.meta.hot) import.meta.hot.accept();`;
         const json = JSON.parse(manifest.source) as Manifest;
 
         for (const item of Object.values(json)) {
-          if (item.isEntry) {
-            serverEntryFilename = item.file;
-          }
-
           if (item.assets) {
             for (let i = 0; i < item.assets.length; i++) {
               const id = item.assets[i];