diff --git a/dwds/debug_extension_mv3/build.yaml b/dwds/debug_extension_mv3/build.yaml
index a1cdac35e..1ef92a8d1 100644
--- a/dwds/debug_extension_mv3/build.yaml
+++ b/dwds/debug_extension_mv3/build.yaml
@@ -8,21 +8,4 @@ targets:
             - --csp
         generate_for:
           - web/**.dart
-      mv3_extension|client_js_copy_builder:
-        enabled: true
-      
-builders:
-  client_js_copy_builder:
-    import: "tool/copy_builder.dart"
-    builder_factories:
-        - copyBuilder
-    build_extensions:
-      {
-        "web/{{}}.dart.js": ["compiled/{{}}.dart.js"],
-        "web/static_assets/{{}}.png": ["compiled/static_assets/{{}}.png"],
-        "web/static_assets/{{}}.html": ["compiled/static_assets/{{}}.html"],
-        "web/static_assets/{{}}.css": ["compiled/static_assets/{{}}.css"],
-        "web/manifest.json": ["compiled/manifest.json"],
-      }
-    auto_apply: none
-    build_to: source
+
diff --git a/dwds/debug_extension_mv3/tool/build_extension.dart b/dwds/debug_extension_mv3/tool/build_extension.dart
index 32e1a2692..d0d30ec60 100644
--- a/dwds/debug_extension_mv3/tool/build_extension.dart
+++ b/dwds/debug_extension_mv3/tool/build_extension.dart
@@ -16,6 +16,7 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:args/args.dart';
+import 'package:io/io.dart';
 import 'package:path/path.dart' as p;
 
 const _prodFlag = 'prod';
@@ -43,13 +44,25 @@ Future<int> run({required bool isProd, required bool isMV3}) async {
   _logInfo('Compiling extension with dart2js to /compiled directory');
   final compileStep = await Process.start(
     'dart',
-    ['run', 'build_runner', 'build', 'web', '--output', 'build', '--release'],
+    [
+      'run',
+      'build_runner',
+      'build',
+      'web',
+      '--output',
+      'build',
+      '--release',
+      '--delete-conflicting-outputs',
+    ],
   );
   final compileExitCode = await _handleProcess(compileStep);
   // Terminate early if compilation failed:
   if (compileExitCode != 0) {
     return compileExitCode;
   }
+
+  _logInfo('Creating /compiled directory if it doesn\'t exist');
+  await Directory('compiled').create();
   final manifestFileName = isMV3 ? 'manifest_mv3' : 'manifest_mv2';
   _logInfo('Copying manifest.json to /compiled directory');
   try {
@@ -61,6 +74,31 @@ Future<int> run({required bool isProd, required bool isMV3}) async {
     // Return non-zero exit code to indicate failure:
     return 1;
   }
+  _logInfo('Copying /static_assets to /compiled directory');
+  try {
+    await copyPath(
+      p.join('web', 'static_assets'),
+      p.join('compiled', 'static_assets'),
+    );
+  } catch (error) {
+    _logWarning('Copying static_assets failed: $error');
+    // Return non-zero exit code to indicate failure:
+    return 1;
+  }
+  _logInfo('Copying generated *.dart.js files to /compiled directory');
+  try {
+    await for (final file in Directory(p.join('build', 'web')).list()) {
+      if (file.path.endsWith('dart.js')) {
+        final fileName = p.split(file.path).last;
+        File(file.path).copySync(p.join('compiled', fileName));
+      }
+    }
+  } catch (error) {
+    _logWarning('Copying *.dart.js files failed: $error');
+    // Return non-zero exit code to indicate failure:
+    return 1;
+  }
+
   // If we're compiling for prod, skip updating the manifest.json:
   if (isProd) return 0;
   // Update manifest.json for dev:
diff --git a/dwds/debug_extension_mv3/tool/copy_builder.dart b/dwds/debug_extension_mv3/tool/copy_builder.dart
deleted file mode 100644
index 4a5e5d04f..000000000
--- a/dwds/debug_extension_mv3/tool/copy_builder.dart
+++ /dev/null
@@ -1,47 +0,0 @@
-// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import 'package:build/build.dart';
-
-/// Factory for the build script.
-Builder copyBuilder(_) => _CopyBuilder();
-
-class _CopyBuilder extends Builder {
-  @override
-  Map<String, List<String>> get buildExtensions => {
-        "web/{{}}.dart.js": ["compiled/{{}}.dart.js"],
-        "web/static_assets/{{}}.png": ["compiled/static_assets/{{}}.png"],
-        "web/static_assets/{{}}.html": ["compiled/static_assets/{{}}.html"],
-        "web/static_assets/{{}}.css": ["compiled/static_assets/{{}}.css"],
-        "web/manifest.json": ["compiled/manifest.json"],
-      };
-
-  @override
-  Future<void> build(BuildStep buildStep) async {
-    final inputAsset = buildStep.inputId;
-    final allowedOutputs = buildStep.allowedOutputs;
-
-    if (allowedOutputs.length != 1) {
-      return;
-    }
-
-    final outputAsset = allowedOutputs.first;
-    await _copyBinaryFile(
-      buildStep,
-      inputAsset: inputAsset,
-      outputAsset: outputAsset,
-    );
-  }
-
-  Future<void> _copyBinaryFile(
-    BuildStep buildStep, {
-    required AssetId inputAsset,
-    required AssetId outputAsset,
-  }) {
-    return buildStep.writeAsBytes(
-      outputAsset,
-      buildStep.readAsBytes(inputAsset),
-    );
-  }
-}