fix(aws): copy server/instrumentation.js into standalone dir on Next.js 16

.changeset/next16-standalone-instrumentation.md

@@ -0,0 +1,13 @@
+---
+"@opennextjs/aws": patch
+---
+
+Fix `server/instrumentation.js does not exist` build failure on Next.js 16
+
+On Next.js 16 the standalone output no longer copies `server/instrumentation.js`
+into the standalone directory, but `copyTracedFiles` copies the instrumentation
+`.nft.json` trace and then asserts the `.js` file exists in the standalone dir,
+throwing `File server/instrumentation.js does not exist` during the server
+bundle. The instrumentation file is now copied from the build dir into the
+standalone dir (mirroring the existing `.nft.json` copy) so the assertion passes
+and the file ships in the bundle.

packages/open-next/src/build/copyTracedFiles.ts

@@ -243,6 +243,20 @@ File ${serverPath} does not exist
       path.join(dotNextDir, INSTRUMENTATION_TRACE_FILE),
       path.join(standaloneNextDir, INSTRUMENTATION_TRACE_FILE),
     );
+    // Next 16's standalone output no longer includes `server/instrumentation.js`
+    // in the standalone dir, but `computeCopyFilesForPage` asserts it exists
+    // there. Copy it from the build dir (mirroring the .nft.json copy above) so
+    // the assertion passes and the instrumentation file ships in the bundle.
+    const instrumentationServerFile = path.join("server", "instrumentation.js");
+    if (
+      existsSync(path.join(dotNextDir, instrumentationServerFile)) &&
+      !existsSync(path.join(standaloneNextDir, instrumentationServerFile))
+    ) {
+      copyFileAndMakeOwnerWritable(
+        path.join(dotNextDir, instrumentationServerFile),
+        path.join(standaloneNextDir, instrumentationServerFile),
+      );
+    }
     computeCopyFilesForPage("instrumentation");
     logger.debug("Adding instrumentation trace files");
   }