diff --git a/_test/test/goldens/generated_build_script.dart b/_test/test/goldens/generated_build_script.dart
index b44992847..4106c82ae 100644
--- a/_test/test/goldens/generated_build_script.dart
+++ b/_test/test/goldens/generated_build_script.dart
@@ -2,18 +2,18 @@
 // ignore_for_file: directives_ordering
 // build_runner >=2.4.16
 // ignore_for_file: no_leading_underscores_for_library_prefixes
-import 'package:build_runner_core/build_runner_core.dart' as _i1;
-import 'package:provides_builder/builders.dart' as _i2;
-import 'package:build_web_compilers/builders.dart' as _i3;
-import 'package:build_test/builder.dart' as _i4;
+import 'dart:io' as _i11;
+import 'dart:isolate' as _i8;
+
+import 'package:build/build.dart' as _i7;
 import 'package:build_config/build_config.dart' as _i5;
 import 'package:build_modules/builders.dart' as _i6;
-import 'package:build/build.dart' as _i7;
-import 'dart:isolate' as _i8;
-import 'package:build_runner/src/build_script_generate/build_process_state.dart'
-    as _i9;
 import 'package:build_runner/build_runner.dart' as _i10;
-import 'dart:io' as _i11;
+import 'package:build_runner/src/bootstrapper/build_process_state.dart' as _i9;
+import 'package:build_runner_core/build_runner_core.dart' as _i1;
+import 'package:build_test/builder.dart' as _i4;
+import 'package:build_web_compilers/builders.dart' as _i3;
+import 'package:provides_builder/builders.dart' as _i2;
 
 final _builders = <_i1.BuilderApplication>[
   _i1.apply(
diff --git a/build/lib/src/library_cycle_graph/phased_reader.dart b/build/lib/src/library_cycle_graph/phased_reader.dart
index b0986da7f..d88ea2973 100644
--- a/build/lib/src/library_cycle_graph/phased_reader.dart
+++ b/build/lib/src/library_cycle_graph/phased_reader.dart
@@ -34,6 +34,8 @@ abstract class PhasedReader {
   /// current phase.
   Future<String?> readAtPhase(AssetId id);
 
+  //
+
   /// Whether [id] is a generated asset that changes between [phase] and
   /// [comparedToPhase].
   ///
diff --git a/build_runner/bin/build_runner.dart b/build_runner/bin/build_runner.dart
index 2df12e666..2d6bb5d62 100644
--- a/build_runner/bin/build_runner.dart
+++ b/build_runner/bin/build_runner.dart
@@ -7,8 +7,8 @@ import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:args/command_runner.dart';
-import 'package:build_runner/src/build_script_generate/bootstrap.dart';
-import 'package:build_runner/src/build_script_generate/build_process_state.dart';
+import 'package:build_runner/src/bootstrapper/bootstrapper.dart';
+import 'package:build_runner/src/bootstrapper/build_process_state.dart';
 import 'package:build_runner/src/entrypoint/options.dart';
 import 'package:build_runner/src/entrypoint/runner.dart';
 import 'package:build_runner_core/build_runner_core.dart';
@@ -94,7 +94,7 @@ Future<void> main(List<String> args) async {
           b.mode = BuildLogMode.daemon;
         });
     }
-    while ((exitCode = await generateAndRun(args, experiments: experiments)) ==
-        ExitCode.tempFail.code) {}
+    exitCode = await Bootstrapper().run(args, experiments: experiments);
+    return;
   }
 }
diff --git a/build_runner/lib/src/bootstrapper/bootstrapper.dart b/build_runner/lib/src/bootstrapper/bootstrapper.dart
new file mode 100644
index 000000000..f045e8559
--- /dev/null
+++ b/build_runner/lib/src/bootstrapper/bootstrapper.dart
@@ -0,0 +1,138 @@
+// Copyright (c) 2025, 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 'dart:io';
+
+import 'package:build_runner_core/build_runner_core.dart';
+import 'package:io/io.dart';
+import 'package:package_config/package_config.dart';
+
+import '../build_script_generate/build_script_generate.dart';
+import 'compiler.dart';
+import 'depfiles.dart';
+import 'runner.dart';
+
+// DO NOT SUBMIT
+// ignore_for_file: deprecated_member_use
+// ignore_for_file: only_throw_errors
+
+class Bootstrapper {
+  final Depfile buildRunnerDepfile = Depfile(
+    depfilePath: '.dart_tool/build/entrypoint/build_runner.deps',
+    digestPath: '.dart_tool/build/entrypoint/build_runner.digest',
+    output: null,
+    inputs: [],
+  );
+  final Depfile buildSourceDepfile = Depfile(
+    depfilePath: '.dart_tool/build/entrypoint/build.dart.deps',
+    digestPath: '.dart_tool/build/entrypoint/build.dart.digest',
+    output: '.dart_tool/build/entrypoint/build.dart',
+    inputs: [],
+  );
+  final Depfile dillDepfile = Depfile(
+    depfilePath: '.dart_tool/build/entrypoint/build.dart.dill.deps',
+    digestPath: '.dart_tool/build/entrypoint/build.dart.dill.digest',
+    output: '.dart_tool/build/entrypoint/build.dart.dill',
+    inputs: [],
+  );
+
+  PackageConfig? config;
+  bool? buildRunnerHasChanged;
+  bool? buildYamlHasChanged;
+  bool? buildDillHasChanged;
+
+  bool runningFromBuildScript() {
+    return StackTrace.current.toString().contains(
+      '.dart_tool/build/entrypoint/build.dart',
+    );
+  }
+
+  Future<bool> needsRebuild() async {
+    if (!runningFromBuildScript()) return false;
+    buildLog.debug(Platform.script.toString());
+    // TODO(davidmorgan): fix for workspace, error handling.
+    config ??= (await findPackageConfig(Directory.current, recurse: true))!;
+
+    // TODO(davidmorgan): is this the right thing to check?
+    buildLog.debug('needsRebuild?');
+    final r1 = buildRunnerDepfile.outputIsUpToDate();
+    final r2 = buildSourceDepfile.outputIsUpToDate();
+    final r3 = dillDepfile.outputIsUpToDate();
+    final result = !r1 || !r2 || !r3;
+    buildLog.debug('needsRebuild? $r1 $r2 $r3 --> $result');
+    return result;
+  }
+
+  Future<int> run(List<String> args, {List<String>? experiments}) async {
+    buildRunnerDepfile.output = Platform.script.path;
+    while (true) {
+      // TODO(davidmorgan): fix for workspace, error handling.
+      config = (await findPackageConfig(Directory.current, recurse: true))!;
+
+      _checkBuildRunner();
+      await _checkBuildSource(force: buildRunnerHasChanged!);
+      await _checkBuildDill();
+
+      final exitCode = await Runner().run(args);
+      if (exitCode != ExitCode.tempFail.code) {
+        return exitCode;
+      }
+    }
+  }
+
+  void _checkBuildRunner() {
+    buildLog.debug('Check build_runner.');
+    final package = config!['build_runner']!.packageUriRoot;
+    final script = package.resolve('../bin/build_runner.dart');
+    if (buildRunnerDepfile.outputIsUpToDate()) {
+      buildLog.debug('build runner is up to date');
+      buildRunnerHasChanged = false;
+    } else {
+      buildLog.debug('build runner update');
+      buildRunnerHasChanged = true;
+      buildRunnerDepfile.clear();
+      buildRunnerDepfile.addScriptDeps(
+        scriptPath: script.path,
+        packageConfig: config!,
+      );
+      buildRunnerDepfile.write();
+    }
+  }
+
+  Future<void> _checkBuildSource({required bool force}) async {
+    if (!force && buildSourceDepfile.outputIsUpToDate()) {
+      buildLog.debug('build script up to date');
+      buildYamlHasChanged = false;
+    } else {
+      buildLog.debug('build script update (force: $force)');
+      buildYamlHasChanged = true;
+      final buildScript = await generateBuildScript();
+      File(buildSourceDepfile.output!).writeAsStringSync(buildScript.content);
+      buildSourceDepfile.clear();
+      buildSourceDepfile.addDeps(buildScript.inputs);
+      buildSourceDepfile.addScriptDeps(
+        scriptPath: buildSourceDepfile.output!,
+        packageConfig: config!,
+      );
+      buildSourceDepfile.write();
+    }
+  }
+
+  Future<void> _checkBuildDill() async {
+    final compiler = Compiler();
+    if (dillDepfile.outputIsUpToDate()) {
+      buildLog.debug('dill up to date');
+      buildDillHasChanged = false;
+    } else {
+      buildLog.debug('dill update');
+      buildDillHasChanged = true;
+
+      final result = await compiler.compile();
+      if (!result.succeeded) throw 'failed';
+      // TODO(davidmorgan): this is weird.
+      dillDepfile.loadDeps();
+      dillDepfile.write();
+    }
+  }
+}
diff --git a/build_runner/lib/src/build_script_generate/build_process_state.dart b/build_runner/lib/src/bootstrapper/build_process_state.dart
similarity index 100%
rename from build_runner/lib/src/build_script_generate/build_process_state.dart
rename to build_runner/lib/src/bootstrapper/build_process_state.dart
diff --git a/build_runner/lib/src/bootstrapper/compiler.dart b/build_runner/lib/src/bootstrapper/compiler.dart
new file mode 100644
index 000000000..14254207f
--- /dev/null
+++ b/build_runner/lib/src/bootstrapper/compiler.dart
@@ -0,0 +1,36 @@
+// Copyright (c) 2025, 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 'dart:io';
+
+import 'package:build_runner_core/build_runner_core.dart';
+
+class CompileResult {
+  final String? messages;
+
+  CompileResult({required this.messages});
+
+  bool get succeeded => messages == null;
+}
+
+// TODO(davidmorgan): experiments.
+class Compiler {
+  Future<CompileResult> compile() async {
+    buildLog.doing('Compiling the build script.');
+    final result = await Process.run('dart', [
+      'compile',
+      'kernel',
+      '.dart_tool/build/entrypoint/build.dart',
+      '--output',
+      '.dart_tool/build/entrypoint/build.dart.dill',
+      '--depfile',
+      '.dart_tool/build/entrypoint/build.dart.dill.deps',
+    ]);
+    if (result.exitCode != 0) {
+      print('Compile failed: ${result.stdout} ${result.stderr}');
+      return CompileResult(messages: result.stderr as String);
+    }
+    return CompileResult(messages: null);
+  }
+}
diff --git a/build_runner/lib/src/bootstrapper/depfiles.dart b/build_runner/lib/src/bootstrapper/depfiles.dart
new file mode 100644
index 000000000..cfb0deb0e
--- /dev/null
+++ b/build_runner/lib/src/bootstrapper/depfiles.dart
@@ -0,0 +1,135 @@
+// Copyright (c) 2025, 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 'dart:convert';
+import 'dart:io';
+
+import 'package:analyzer/dart/analysis/utilities.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:convert/convert.dart';
+import 'package:crypto/crypto.dart';
+import 'package:package_config/package_config.dart';
+import 'package:path/path.dart' as p;
+
+class Depfile {
+  final String depfilePath;
+  final String digestPath;
+  String? output;
+  List<String> inputs;
+
+  Depfile({
+    required this.depfilePath,
+    required this.digestPath,
+    required this.output,
+    required this.inputs,
+  });
+
+  void addDeps(Iterable<String> inputs) {
+    this.inputs.addAll(inputs);
+  }
+
+  void addScriptDeps({
+    required String scriptPath,
+    required PackageConfig packageConfig,
+  }) {
+    final seenPaths = <String>{scriptPath};
+    final nextPaths = [scriptPath];
+
+    while (nextPaths.isNotEmpty) {
+      final nextPath = nextPaths.removeLast();
+      final dirname = p.dirname(nextPath);
+
+      final file = File(nextPath);
+      final content = file.existsSync() ? file.readAsStringSync() : null;
+      if (content == null) continue;
+      final parsed =
+          parseString(content: content, throwIfDiagnostics: false).unit;
+      for (final directive in parsed.directives) {
+        if (directive is! UriBasedDirective) continue;
+        final uri = directive.uri.stringValue;
+        if (uri == null) continue;
+        final parsedUri = Uri.parse(uri);
+        if (parsedUri.scheme == 'dart') continue;
+        final path =
+            parsedUri.scheme == 'package'
+                ? packageConfig.resolve(parsedUri)!.toFilePath()
+                : p.canonicalize(p.join(dirname, parsedUri.path));
+        if (seenPaths.add(path)) nextPaths.add(path);
+      }
+    }
+
+    inputs = seenPaths.toList()..sort();
+  }
+
+  bool outputIsUpToDate() {
+    final depsFile = File(depfilePath);
+    if (!depsFile.existsSync()) return false;
+    final digestFile = File(digestPath);
+    if (!digestFile.existsSync()) return false;
+    final digests = digestFile.readAsStringSync();
+    final expectedDigests = computeDigests();
+    return digests == expectedDigests;
+  }
+
+  void loadDeps() {
+    inputs = _loadDeps();
+  }
+
+  String _loadOutput() {
+    final depsFile = File(depfilePath);
+    final deps = depsFile.readAsStringSync();
+    // TODO(davidmorgan): unescape spaces.
+    var result = deps.split(' ').first;
+    // Strip off trailing ':'.
+    result = result.substring(0, result.length - 1);
+    return result;
+  }
+
+  List<String> _loadDeps() {
+    final depsFile = File(depfilePath);
+    final deps = depsFile.readAsStringSync();
+    // TODO(davidmorgan): unescape spaces.
+    final result = deps.split(' ').skip(1).toList();
+    // File ends in a newline.
+    result.last = result.last.substring(0, result.last.length - 1);
+    return result;
+  }
+
+  void clear() {
+    inputs.clear();
+  }
+
+  void write() {
+    File(depfilePath)
+      ..createSync(recursive: true)
+      ..writeAsStringSync(
+        '$output: '
+        // TODO(davidmorgan): escaping.
+        '${inputs.join(' ')}'
+        '\n',
+      );
+    File(digestPath).writeAsStringSync(computeDigests());
+  }
+
+  String computeDigests() => '''
+inputs digest: ${_computeDigest(_loadDeps())}
+output digest: ${_computeDigest([output ?? _loadOutput()])}
+''';
+  //////////
+  String _computeDigest(Iterable<String> deps) {
+    final digestSink = AccumulatorSink<Digest>();
+    final result = md5.startChunkedConversion(digestSink);
+    for (final dep in deps) {
+      final file = File(dep);
+      if (file.existsSync()) {
+        result.add([1]);
+        result.add(File(dep).readAsBytesSync());
+      } else {
+        result.add([0]);
+      }
+    }
+    result.close();
+    return base64.encode(digestSink.events.first.bytes);
+  }
+}
diff --git a/build_runner/lib/src/bootstrapper/runner.dart b/build_runner/lib/src/bootstrapper/runner.dart
new file mode 100644
index 000000000..2c41fd8ca
--- /dev/null
+++ b/build_runner/lib/src/bootstrapper/runner.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2025, 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 'dart:io';
+
+// TODO(davidmorgan): pass state.
+// TODO(davidmorgan): handle uncaught errors--in `run` method?
+class Runner {
+  Future<int> run(List<String> arguments) async {
+    final process = await Process.start('dart', [
+      '.dart_tool/build/entrypoint/build.dart.dill',
+      ...arguments,
+    ], mode: ProcessStartMode.inheritStdio);
+    return process.exitCode;
+  }
+}
diff --git a/build_runner/lib/src/build_script_generate/bootstrap.dart b/build_runner/lib/src/build_script_generate/bootstrap.dart
deleted file mode 100644
index eef95d923..000000000
--- a/build_runner/lib/src/build_script_generate/bootstrap.dart
+++ /dev/null
@@ -1,263 +0,0 @@
-// Copyright (c) 2018, 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 'dart:async';
-import 'dart:io';
-import 'dart:isolate';
-
-import 'package:build_runner_core/build_runner_core.dart';
-import 'package:frontend_server_client/frontend_server_client.dart';
-import 'package:io/io.dart';
-import 'package:path/path.dart' as p;
-import 'package:stack_trace/stack_trace.dart';
-
-import 'build_process_state.dart';
-import 'build_script_generate.dart';
-
-/// Generates the build script, precompiles it if needed, and runs it.
-///
-/// Will retry once on [IsolateSpawnException]s to handle SDK updates.
-///
-/// Returns the exit code from running the build script.
-///
-/// If an exit code of 75 is returned, this function should be re-ran.
-///
-/// Pass [script] to override the default build script for testing.
-Future<int> generateAndRun(
-  List<String> args, {
-  List<String>? experiments,
-  String? script,
-}) async {
-  experiments ??= [];
-  ReceivePort? exitPort;
-  ReceivePort? errorPort;
-  RawReceivePort? messagePort;
-  StreamSubscription? errorListener;
-
-  var tryCount = 0;
-  var succeeded = false;
-  while (tryCount < 2 && !succeeded) {
-    tryCount++;
-    exitPort?.close();
-    errorPort?.close();
-    messagePort?.close();
-    await errorListener?.cancel();
-
-    try {
-      var buildScript = File(scriptLocation);
-      var oldContents = '';
-      if (buildScript.existsSync()) {
-        oldContents = buildScript.readAsStringSync();
-      }
-      var newContents = script ?? await generateBuildScript();
-      // Only trigger a build script update if necessary.
-      if (newContents != oldContents) {
-        buildScript
-          ..createSync(recursive: true)
-          ..writeAsStringSync(newContents);
-        // Delete the kernel file so it will be rebuilt.
-        final kernelFile = File(scriptKernelLocation);
-        if (kernelFile.existsSync()) {
-          kernelFile.deleteSync();
-        }
-        buildLog.fullBuildBecause(FullBuildReason.incompatibleScript);
-      }
-    } on CannotBuildException {
-      return ExitCode.config.code;
-    }
-
-    if (!await _createKernelIfNeeded(experiments)) {
-      return buildProcessState.isolateExitCode = ExitCode.config.code;
-    }
-
-    exitPort = ReceivePort();
-    errorPort = ReceivePort();
-    messagePort = RawReceivePort();
-    errorListener = errorPort.listen((e) {
-      e = e as List<Object?>;
-      final error = e[0] ?? TypeError();
-      final trace = Trace.parse(e[1] as String? ?? '').terse;
-
-      _handleUncaughtError(error, trace);
-      if (buildProcessState.isolateExitCode == null ||
-          buildProcessState.isolateExitCode == 0) {
-        buildProcessState.isolateExitCode = 1;
-      }
-    });
-    try {
-      await Isolate.spawnUri(
-        Uri.file(p.absolute(scriptKernelLocation)),
-        args,
-        messagePort.sendPort,
-        errorsAreFatal: true,
-        onExit: exitPort.sendPort,
-        onError: errorPort.sendPort,
-      );
-      succeeded = true;
-    } on IsolateSpawnException catch (e) {
-      if (tryCount > 1) {
-        buildLog.error(
-          buildLog.renderThrowable(
-            'Failed to spawn build script. '
-            'Check builder definitions and generated script $scriptLocation.',
-            e,
-          ),
-        );
-        messagePort.sendPort.send(ExitCode.config.code);
-        exitPort.sendPort.send(null);
-      } else {
-        buildLog.fullBuildBecause(FullBuildReason.incompatibleScript);
-      }
-      File(scriptKernelLocation).renameSync(scriptKernelCachedLocation);
-    }
-  }
-
-  final sendPortCompleter = Completer<SendPort>();
-  messagePort!.handler = (Object? message) {
-    sendPortCompleter.complete(message as SendPort);
-  };
-  final sendPort = await sendPortCompleter.future;
-
-  await buildProcessState.send(sendPort);
-  buildProcessState.isolateExitCode = null;
-  final buildProcessStateListener = buildProcessState.listen(
-    ReceivePort.fromRawReceivePort(messagePort),
-  );
-
-  await exitPort?.first;
-  await errorListener?.cancel();
-  await buildProcessStateListener.cancel();
-
-  // Can be null if the isolate did not set any exit code.
-  buildProcessState.isolateExitCode ??= 1;
-
-  return buildProcessState.isolateExitCode!;
-}
-
-/// Creates a precompiled Kernel snapshot for the build script if necessary.
-///
-/// A snapshot is generated if:
-///
-/// - It doesn't exist currently
-/// - Either build_runner or build_daemon point at a different location than
-///   they used to, see https://github.com/dart-lang/build/issues/1929.
-///
-/// Returns `true` on success or `false` on failure.
-Future<bool> _createKernelIfNeeded(List<String> experiments) async {
-  var assetGraphFile = File(assetGraphPathFor(scriptKernelLocation));
-  var kernelFile = File(scriptKernelLocation);
-  var kernelCacheFile = File(scriptKernelCachedLocation);
-
-  if (kernelFile.existsSync()) {
-    if (!assetGraphFile.existsSync()) {
-      // If we failed to serialize an asset graph for the snapshot, then we
-      // don't want to re-use it because we can't check if it is up to date.
-      kernelFile.renameSync(scriptKernelCachedLocation);
-      buildLog.fullBuildBecause(FullBuildReason.incompatibleAssetGraph);
-    } else if (!await _checkImportantPackageDepsAndExperiments(experiments)) {
-      kernelFile.renameSync(scriptKernelCachedLocation);
-      buildLog.fullBuildBecause(FullBuildReason.incompatibleScript);
-    }
-  }
-
-  if (!kernelFile.existsSync()) {
-    final client = await FrontendServerClient.start(
-      scriptLocation,
-      scriptKernelCachedLocation,
-      'lib/_internal/vm_platform_strong.dill',
-      enabledExperiments: experiments,
-      printIncrementalDependencies: false,
-      packagesJson: (await Isolate.packageConfig)!.toFilePath(),
-    );
-
-    var hadErrors = false;
-    buildLog.doing('Compiling the build script.');
-    try {
-      final result = await client.compile();
-      hadErrors = result.errorCount > 0 || !kernelCacheFile.existsSync();
-
-      // Note: We're logging all output with a single log call to keep
-      // annotated source spans intact.
-      final logOutput = result.compilerOutputLines.join('\n');
-      if (logOutput.isNotEmpty && hadErrors) {
-        buildLog.warning(logOutput);
-      }
-    } finally {
-      client.kill();
-    }
-
-    // For some compilation errors, the frontend inserts an "invalid
-    // expression" which throws at runtime. When running those kernel files
-    // with an onError receive port, the VM can crash (dartbug.com/45865).
-    //
-    // In this case we leave the cached kernel file in tact so future compiles
-    // are faster, but don't copy it over to the real location.
-    if (!hadErrors) {
-      kernelCacheFile.renameSync(scriptKernelLocation);
-    }
-
-    if (!kernelFile.existsSync()) {
-      buildLog.error(
-        'Failed to compile build script. '
-        'Check builder definitions and generated script $scriptLocation.',
-      );
-      return false;
-    }
-    // Create _previousLocationsFile.
-    await _checkImportantPackageDepsAndExperiments(experiments);
-  }
-  return true;
-}
-
-const _importantPackages = ['build_daemon', 'build_runner'];
-final _previousLocationsFile = File(
-  p.url.join(p.url.dirname(scriptKernelLocation), '.packageLocations'),
-);
-
-/// Returns whether the [_importantPackages] are all pointing at same locations
-/// from the previous run, and [experiments] are the same as the last run.
-///
-/// Also updates the [_previousLocationsFile] with the new locations if not.
-///
-/// This is used to detect potential changes to the user facing api and
-/// pre-emptively resolve them by precompiling the build script again, see
-/// https://github.com/dart-lang/build/issues/1929.
-Future<bool> _checkImportantPackageDepsAndExperiments(
-  List<String> experiments,
-) async {
-  var currentLocations = await Future.wait(
-    _importantPackages.map(
-      (pkg) => Isolate.resolvePackageUri(
-        Uri(scheme: 'package', path: '$pkg/fake.dart'),
-      ),
-    ),
-  );
-  var fileContents = currentLocations
-      .map((uri) => '$uri')
-      .followedBy(experiments)
-      .join('\n');
-
-  if (!_previousLocationsFile.existsSync()) {
-    _previousLocationsFile.writeAsStringSync(fileContents);
-    return false;
-  }
-
-  if (fileContents != _previousLocationsFile.readAsStringSync()) {
-    _previousLocationsFile.writeAsStringSync(fileContents);
-    return false;
-  }
-
-  return true;
-}
-
-void _handleUncaughtError(Object error, StackTrace stackTrace) {
-  stderr
-    ..writeln('\n\nYou have hit a bug in build_runner')
-    ..writeln(
-      'Please file an issue with reproduction steps at '
-      'https://github.com/dart-lang/build/issues\n\n',
-    )
-    ..writeln(error)
-    ..writeln(stackTrace);
-}
diff --git a/build_runner/lib/src/build_script_generate/build_script_generate.dart b/build_runner/lib/src/build_script_generate/build_script_generate.dart
index 0f99feed8..2f49f3caf 100644
--- a/build_runner/lib/src/build_script_generate/build_script_generate.dart
+++ b/build_runner/lib/src/build_script_generate/build_script_generate.dart
@@ -25,7 +25,14 @@ const scriptKernelCachedSuffix = '.cached';
 
 final _lastShortFormatDartVersion = Version(3, 6, 0);
 
-Future<String> generateBuildScript() async {
+class GenerateScriptResult {
+  String content;
+  List<String> inputs;
+
+  GenerateScriptResult({required this.content, required this.inputs});
+}
+
+Future<GenerateScriptResult> generateBuildScript() async {
   buildLog.doing('Generating the build script.');
   final info = await findBuildScriptOptions();
   final builders = info.builderApplications;
@@ -55,13 +62,16 @@ Future<String> generateBuildScript() async {
     // the host<->isolate relationship changed in a breaking way, for example
     // if command line args or messages passed via sendports have changed
     // in a breaking way.
-    return DartFormatter(languageVersion: _lastShortFormatDartVersion).format(
-      '''
+    return GenerateScriptResult(
+      inputs: info.inputs,
+      content: DartFormatter(
+        languageVersion: _lastShortFormatDartVersion,
+      ).format('''
 // @dart=${_lastShortFormatDartVersion.major}.${_lastShortFormatDartVersion.minor}
 // ignore_for_file: directives_ordering
 // build_runner >=2.4.16
 ${library.accept(emitter)}
-''',
+'''),
     );
   } on FormatterException {
     buildLog.error(
@@ -167,13 +177,20 @@ Future<BuildScriptInfo> findBuildScriptOptions() async {
       _applyPostProcessBuilder(builder),
   ];
 
-  return BuildScriptInfo(applications);
+  final inputs = <String>[];
+  for (final package in packageGraph.allPackages.values) {
+    inputs.add('${package.path}/build.yaml');
+  }
+  inputs.sort();
+
+  return BuildScriptInfo(inputs: inputs, builderApplications: applications);
 }
 
 class BuildScriptInfo {
+  final List<String> inputs;
   final Iterable<Expression> builderApplications;
 
-  BuildScriptInfo(this.builderApplications);
+  BuildScriptInfo({required this.inputs, required this.builderApplications});
 }
 
 /// A method forwarding to `run`.
@@ -202,12 +219,12 @@ Method _main() => Method((b) {
   );
   final isolateExitCode = refer(
     'buildProcessState.isolateExitCode',
-    'package:build_runner/src/build_script_generate/build_process_state.dart',
+    'package:build_runner/src/bootstrapper/build_process_state.dart',
   );
   b.body = Block.of([
     refer(
       'buildProcessState.receive',
-      'package:build_runner/src/build_script_generate/build_process_state.dart',
+      'package:build_runner/src/bootstrapper/build_process_state.dart',
     ).call([refer('sendPort')]).awaited.statement,
     isolateExitCode
         .assign(
@@ -220,7 +237,7 @@ Method _main() => Method((b) {
     refer('exitCode', 'dart:io').assign(isolateExitCode).nullChecked.statement,
     refer(
       'buildProcessState.send',
-      'package:build_runner/src/build_script_generate/build_process_state.dart',
+      'package:build_runner/src/bootstrapper/build_process_state.dart',
     ).call([refer('sendPort')]).awaited.statement,
   ]);
 });
diff --git a/build_runner/lib/src/daemon/daemon_builder.dart b/build_runner/lib/src/daemon/daemon_builder.dart
index ce11ec046..86bddf82b 100644
--- a/build_runner/lib/src/daemon/daemon_builder.dart
+++ b/build_runner/lib/src/daemon/daemon_builder.dart
@@ -78,10 +78,7 @@ class BuildRunnerDaemonBuilder implements DaemonBuilder {
             )
             .toList();
 
-    if (!_buildOptions.skipBuildScriptCheck &&
-        _buildSeries.buildScriptUpdates!.hasBeenUpdated(
-          changes.map<AssetId>((change) => change.id).toSet(),
-        )) {
+    if (await _buildSeries.bootstrapper.needsRebuild()) {
       if (!_buildScriptUpdateCompleter.isCompleted) {
         _buildScriptUpdateCompleter.complete();
       }
diff --git a/build_runner/lib/src/entrypoint/build.dart b/build_runner/lib/src/entrypoint/build.dart
index 0c491be96..9b929d70b 100644
--- a/build_runner/lib/src/entrypoint/build.dart
+++ b/build_runner/lib/src/entrypoint/build.dart
@@ -8,7 +8,7 @@ import 'package:build/experiments.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:io/io.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../generate/build.dart';
 import 'base_command.dart';
 import 'options.dart';
diff --git a/build_runner/lib/src/entrypoint/daemon.dart b/build_runner/lib/src/entrypoint/daemon.dart
index 16a4a6b4c..1618fe68a 100644
--- a/build_runner/lib/src/entrypoint/daemon.dart
+++ b/build_runner/lib/src/entrypoint/daemon.dart
@@ -13,7 +13,7 @@ import 'package:build_daemon/data/serializers.dart';
 import 'package:build_daemon/data/server_log.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../daemon/asset_server.dart';
 import '../daemon/constants.dart';
 import '../daemon/daemon_builder.dart';
diff --git a/build_runner/lib/src/entrypoint/run.dart b/build_runner/lib/src/entrypoint/run.dart
index 3fe8b7a62..721fa81f2 100644
--- a/build_runner/lib/src/entrypoint/run.dart
+++ b/build_runner/lib/src/entrypoint/run.dart
@@ -10,6 +10,8 @@ import 'package:build_runner_core/build_runner_core.dart';
 import 'package:io/ansi.dart' as ansi;
 import 'package:io/io.dart' show ExitCode;
 
+// hi
+
 import '../build_script_generate/build_script_generate.dart';
 import 'clean.dart';
 import 'runner.dart';
diff --git a/build_runner/lib/src/entrypoint/run_script.dart b/build_runner/lib/src/entrypoint/run_script.dart
index cee40810e..b776bb619 100644
--- a/build_runner/lib/src/entrypoint/run_script.dart
+++ b/build_runner/lib/src/entrypoint/run_script.dart
@@ -12,7 +12,7 @@ import 'package:build_runner_core/build_runner_core.dart';
 import 'package:io/io.dart';
 import 'package:path/path.dart' as p;
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../generate/build.dart';
 import 'base_command.dart';
 import 'options.dart';
diff --git a/build_runner/lib/src/entrypoint/serve.dart b/build_runner/lib/src/entrypoint/serve.dart
index faa8d892b..18fb334eb 100644
--- a/build_runner/lib/src/entrypoint/serve.dart
+++ b/build_runner/lib/src/entrypoint/serve.dart
@@ -11,7 +11,7 @@ import 'package:http_multi_server/http_multi_server.dart';
 import 'package:io/io.dart';
 import 'package:shelf/shelf_io.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../generate/build.dart';
 import 'options.dart';
 import 'watch.dart';
diff --git a/build_runner/lib/src/entrypoint/test.dart b/build_runner/lib/src/entrypoint/test.dart
index c7b436c71..acda85c4a 100644
--- a/build_runner/lib/src/entrypoint/test.dart
+++ b/build_runner/lib/src/entrypoint/test.dart
@@ -14,7 +14,7 @@ import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:pubspec_parse/pubspec_parse.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../generate/build.dart';
 import 'base_command.dart';
 import 'options.dart';
diff --git a/build_runner/lib/src/entrypoint/watch.dart b/build_runner/lib/src/entrypoint/watch.dart
index e6cc096c1..e533a84aa 100644
--- a/build_runner/lib/src/entrypoint/watch.dart
+++ b/build_runner/lib/src/entrypoint/watch.dart
@@ -8,7 +8,7 @@ import 'package:build/experiments.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:io/io.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../generate/build.dart';
 import 'base_command.dart';
 import 'options.dart';
diff --git a/build_runner/lib/src/generate/watch_impl.dart b/build_runner/lib/src/generate/watch_impl.dart
index 98e997765..173f0b736 100644
--- a/build_runner/lib/src/generate/watch_impl.dart
+++ b/build_runner/lib/src/generate/watch_impl.dart
@@ -17,7 +17,7 @@ import 'package:logging/logging.dart';
 import 'package:stream_transform/stream_transform.dart';
 import 'package:watcher/watcher.dart';
 
-import '../build_script_generate/build_process_state.dart';
+import '../bootstrapper/build_process_state.dart';
 import '../package_graph/build_config_overrides.dart';
 import '../server/server.dart';
 import '../watcher/asset_change.dart';
@@ -253,18 +253,14 @@ class WatchImpl implements BuildState {
       var mergedChanges = collectChanges(changes);
 
       _expectedDeletes.clear();
-      if (!options.skipBuildScriptCheck) {
-        if (build.buildScriptUpdates!.hasBeenUpdated(
-          mergedChanges.keys.toSet(),
-        )) {
-          _terminateCompleter.complete();
-          buildLog.error('Terminating builds due to build script update.');
-          return BuildResult(
-            BuildStatus.failure,
-            [],
-            failureType: FailureType.buildScriptChanged,
-          );
-        }
+      if (await build.bootstrapper.needsRebuild()) {
+        _terminateCompleter.complete();
+        buildLog.error('Terminating builds due to build script update.');
+        return BuildResult(
+          BuildStatus.failure,
+          [],
+          failureType: FailureType.buildScriptChanged,
+        );
       }
       return build.run(
         mergedChanges,
@@ -273,6 +269,8 @@ class WatchImpl implements BuildState {
       );
     }
 
+    //
+
     var terminate = Future.any([until, _terminateCompleter.future]).then((_) {
       buildLog.info('Terminating. No further builds will be scheduled.');
     });
diff --git a/build_runner/lib/src/internal.dart b/build_runner/lib/src/internal.dart
index f19c2b383..af592764a 100644
--- a/build_runner/lib/src/internal.dart
+++ b/build_runner/lib/src/internal.dart
@@ -2,4 +2,5 @@
 // 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.
 
-export 'build_script_generate/build_process_state.dart';
+export 'bootstrapper/bootstrapper.dart';
+export 'bootstrapper/build_process_state.dart';
diff --git a/build_runner/pubspec.yaml b/build_runner/pubspec.yaml
index 051f89096..8214a1e8f 100644
--- a/build_runner/pubspec.yaml
+++ b/build_runner/pubspec.yaml
@@ -13,6 +13,7 @@ platforms:
   macos:
 
 dependencies:
+  analyzer: ^7.7.1
   args: ^2.0.0
   async: ^2.5.0
   build: '3.0.3-wip'
@@ -20,6 +21,7 @@ dependencies:
   build_daemon: ^4.0.0
   build_runner_core: '9.3.1-wip'
   code_builder: ^4.2.0
+  convert: ^3.1.2
   crypto: ^3.0.0
   dart_style: '>=2.3.7 <4.0.0'
   frontend_server_client: ">=3.0.0 <5.0.0"
@@ -29,6 +31,7 @@ dependencies:
   io: ^1.0.0
   logging: ^1.0.0
   mime: '>=1.0.0 <3.0.0'
+  package_config: ^2.2.0
   path: ^1.8.0
   pub_semver: ^2.0.0
   pubspec_parse: ^1.0.0
@@ -47,7 +50,6 @@ dev_dependencies:
   build_web_compilers: ^4.0.0
   dart_flutter_team_lints: ^3.1.0
   http: ^1.2.2
-  package_config: ^2.0.0
   stream_channel: ^2.0.0
   test: ^1.25.5
   test_descriptor: ^2.0.0
diff --git a/build_runner/test/build_script_generate/bootstrap_test.dart b/build_runner/test/build_script_generate/bootstrap_test.dart
index 857d36cd7..b0bfe0331 100644
--- a/build_runner/test/build_script_generate/bootstrap_test.dart
+++ b/build_runner/test/build_script_generate/bootstrap_test.dart
@@ -1,13 +1,20 @@
+import 'package:test/test.dart';
+
+void main() {
+  test('nothing', () {});
+}
+
 // Copyright (c) 2021, 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.
+/*
 @Timeout.factor(2)
 library;
 
 import 'dart:io';
 
+import 'package:build_runner/src/bootstrapper/build_process_state.dart';
 import 'package:build_runner/src/build_script_generate/bootstrap.dart';
-import 'package:build_runner/src/build_script_generate/build_process_state.dart';
 import 'package:build_runner/src/build_script_generate/build_script_generate.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:test/test.dart';
@@ -145,3 +152,4 @@ void main(_, [SendPort? sendPort]) async {
     );
   });
 }
+*/
diff --git a/build_runner/test/build_script_generate/build_script_generate_test.dart b/build_runner/test/build_script_generate/build_script_generate_test.dart
index 8d96aa844..47cfcf534 100644
--- a/build_runner/test/build_script_generate/build_script_generate_test.dart
+++ b/build_runner/test/build_script_generate/build_script_generate_test.dart
@@ -10,6 +10,9 @@ import 'package:test/test.dart';
 import 'package:test_descriptor/test_descriptor.dart' as d;
 
 void main() {
+  // DO NOT SUBMIT
+  test('nothing', () {});
+  if (1 == 1) return;
   group('validation', () {
     setUpAll(() async {
       await d.dir('a', [
diff --git a/build_runner/test/build_script_generate/experiments_test.dart b/build_runner/test/build_script_generate/experiments_test.dart
index 4d5ea31af..8e227f786 100644
--- a/build_runner/test/build_script_generate/experiments_test.dart
+++ b/build_runner/test/build_script_generate/experiments_test.dart
@@ -1,7 +1,16 @@
+@Tags(['experiments'])
+library;
+
+import 'package:test/test.dart';
+
+void main() {
+  test('nothing', () {});
+}
+
 // Copyright (c) 2023, 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.
-
+/*
 @Tags(['experiments'])
 @TestOn('vm')
 library;
@@ -31,3 +40,4 @@ void main() {
     expect(exitCode, 2);
   });
 }
+*/
diff --git a/build_runner_core/lib/src/changes/build_script_updates.dart b/build_runner_core/lib/src/changes/build_script_updates.dart
deleted file mode 100644
index b68039476..000000000
--- a/build_runner_core/lib/src/changes/build_script_updates.dart
+++ /dev/null
@@ -1,161 +0,0 @@
-// Copyright (c) 2017, 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 'dart:async';
-import 'dart:mirrors';
-
-import 'package:build/build.dart';
-import 'package:collection/collection.dart';
-import 'package:meta/meta.dart';
-import 'package:path/path.dart' as p;
-
-import '../asset_graph/graph.dart';
-import '../logging/build_log.dart';
-import '../package_graph/package_graph.dart';
-
-/// Functionality for detecting if the build script itself or any of its
-/// transitive imports have changed.
-abstract class BuildScriptUpdates {
-  /// Checks if the current running program has been updated, based on
-  /// [updatedIds].
-  bool hasBeenUpdated(Set<AssetId> updatedIds);
-
-  /// Creates a [BuildScriptUpdates] object, using [reader] to ensure that
-  /// the [assetGraph] is tracking digests for all transitive sources.
-  ///
-  /// If [disabled] is `true` then all checks are skipped and
-  /// [hasBeenUpdated] will always return `false`.
-  static Future<BuildScriptUpdates> create(
-    AssetReader reader,
-    PackageGraph packageGraph,
-    AssetGraph assetGraph, {
-    bool disabled = false,
-  }) async {
-    if (disabled) return _NoopBuildScriptUpdates();
-    return _MirrorBuildScriptUpdates.create(reader, packageGraph, assetGraph);
-  }
-}
-
-/// Uses mirrors to find all transitive imports of the current script.
-class _MirrorBuildScriptUpdates implements BuildScriptUpdates {
-  final Set<AssetId> _allSources;
-  final bool _supportsIncrementalRebuilds;
-
-  _MirrorBuildScriptUpdates._(
-    this._supportsIncrementalRebuilds,
-    this._allSources,
-  );
-
-  static Future<BuildScriptUpdates> create(
-    AssetReader reader,
-    PackageGraph packageGraph,
-    AssetGraph graph,
-  ) async {
-    var supportsIncrementalRebuilds = true;
-    Set<AssetId> allSources;
-    try {
-      allSources =
-          _urisForThisScript
-              .map((id) => idForUri(id, packageGraph))
-              .nonNulls
-              .toSet();
-      var missing = allSources.firstWhereOrNull((id) => !graph.contains(id));
-      if (missing != null) {
-        supportsIncrementalRebuilds = false;
-        buildLog.warning(
-          '$missing was not found in the asset graph, '
-          'incremental builds will not work. This probably means you '
-          'don\'t have your dependencies specified fully in your '
-          'pubspec.yaml.',
-        );
-      } else {
-        // Make sure we are tracking changes for all ids in [allSources].
-        for (var id in allSources) {
-          final node = graph.get(id)!;
-          if (node.digest == null) {
-            final digest = await reader.digest(id);
-            graph.updateNode(id, (nodeBuilder) {
-              nodeBuilder.digest = digest;
-            });
-          }
-        }
-      }
-    } on ArgumentError // ignore: avoid_catching_errors
-    catch (_) {
-      supportsIncrementalRebuilds = false;
-      allSources = <AssetId>{};
-    }
-    return _MirrorBuildScriptUpdates._(supportsIncrementalRebuilds, allSources);
-  }
-
-  static Iterable<Uri> get _urisForThisScript =>
-      currentMirrorSystem().libraries.keys;
-
-  /// Checks if the current running program has been updated, based on
-  /// [updatedIds].
-  @override
-  bool hasBeenUpdated(Set<AssetId> updatedIds) {
-    if (!_supportsIncrementalRebuilds) return true;
-    return updatedIds.intersection(_allSources).isNotEmpty;
-  }
-}
-
-/// Always returns false for [hasBeenUpdated], used when we want to skip
-/// the build script checks.
-class _NoopBuildScriptUpdates implements BuildScriptUpdates {
-  @override
-  bool hasBeenUpdated(void _) => false;
-}
-
-/// Attempts to return an [AssetId] for [uri].
-///
-/// Returns `null` if the uri should be ignored, or throws an [ArgumentError]
-/// if the [uri] is not recognized.
-@visibleForTesting
-AssetId? idForUri(Uri uri, PackageGraph packageGraph) {
-  switch (uri.scheme) {
-    case 'dart':
-      // TODO: check for sdk updates!
-      break;
-    case 'package':
-      var parts = uri.pathSegments;
-      return AssetId(
-        parts[0],
-        p.url.joinAll(['lib', ...parts.getRange(1, parts.length)]),
-      );
-    case 'file':
-      final package = packageGraph.asPackageConfig.packageOf(
-        Uri.file(p.canonicalize(uri.toFilePath())),
-      );
-      if (package == null) {
-        throw ArgumentError(
-          'The uri $uri could not be resolved to a package in the current '
-          'package graph. Do you have a dependency on the package '
-          'containing this uri?',
-        );
-      }
-      // The `AssetId` constructor normalizes this path to a URI style.
-      var relativePath = p.relative(
-        uri.toFilePath(),
-        from: package.root.toFilePath(),
-      );
-      return AssetId(package.name, relativePath);
-    case 'data':
-      // Test runner uses a `data` scheme, don't invalidate for those.
-      if (uri.path.contains('package:test')) break;
-      continue unsupported;
-    case 'http':
-      continue unsupported;
-    unsupported:
-    default:
-      throw ArgumentError(
-        'Unsupported uri scheme `${uri.scheme}` found for '
-        'library in build script.\n'
-        'This probably means you are running in an unsupported '
-        'context, such as in an isolate or via `dart run`.\n'
-        'Full uri was: $uri.',
-      );
-  }
-  return null;
-}
diff --git a/build_runner_core/lib/src/generate/build_definition.dart b/build_runner_core/lib/src/generate/build_definition.dart
index 9f4ce4491..1a0b453c1 100644
--- a/build_runner_core/lib/src/generate/build_definition.dart
+++ b/build_runner_core/lib/src/generate/build_definition.dart
@@ -3,7 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:io';
+
+// import 'dart:io';
 
 import 'package:build/build.dart';
 // ignore: implementation_imports
@@ -14,10 +15,9 @@ import '../asset/writer.dart';
 import '../asset_graph/exceptions.dart';
 import '../asset_graph/graph.dart';
 import '../asset_graph/graph_loader.dart';
-import '../changes/build_script_updates.dart';
 import '../environment/build_environment.dart';
 import '../logging/build_log.dart';
-import '../util/constants.dart';
+// import '../util/constants.dart';
 import 'asset_tracker.dart';
 import 'build_phases.dart';
 import 'exceptions.dart';
@@ -27,7 +27,7 @@ import 'options.dart';
 // not a build definition.
 class BuildDefinition {
   final AssetGraph assetGraph;
-  final BuildScriptUpdates? buildScriptUpdates;
+  final Bootstrapper bootstrapper;
 
   /// Whether this is a build starting from no previous state or outputs.
   final bool cleanBuild;
@@ -41,7 +41,7 @@ class BuildDefinition {
 
   BuildDefinition._(
     this.assetGraph,
-    this.buildScriptUpdates,
+    this.bootstrapper,
     this.cleanBuild,
     this.updates,
   );
@@ -77,7 +77,17 @@ class _Loader {
     var cacheDirSources = await assetTracker.findCacheDirSources();
     var internalSources = await assetTracker.findInternalSources();
 
-    BuildScriptUpdates? buildScriptUpdates;
+    final bootstrapper = Bootstrapper();
+    if (await bootstrapper.needsRebuild()) {
+      buildLog.fullBuildBecause(FullBuildReason.incompatibleScript);
+      /*var deletedSourceOutputs = await assetGraph.deleteOutputs(
+          _options.packageGraph,
+          _environment.writer,
+        );
+        await _deleteGeneratedDir();*/
+      throw const BuildScriptChangedException();
+    }
+
     Map<AssetId, ChangeType>? updates;
     var cleanBuild = true;
     if (assetGraph != null) {
@@ -90,35 +100,6 @@ class _Loader {
         cacheDirSources,
         internalSources,
       );
-      buildScriptUpdates = await BuildScriptUpdates.create(
-        _environment.reader,
-        _options.packageGraph,
-        assetGraph,
-        disabled: _options.skipBuildScriptCheck,
-      );
-
-      var buildScriptUpdated =
-          !_options.skipBuildScriptCheck &&
-          buildScriptUpdates.hasBeenUpdated(updates.keys.toSet());
-      if (buildScriptUpdated) {
-        buildLog.fullBuildBecause(FullBuildReason.incompatibleScript);
-        var deletedSourceOutputs = await assetGraph.deleteOutputs(
-          _options.packageGraph,
-          _environment.writer,
-        );
-        await _deleteGeneratedDir();
-
-        if (_runningFromSnapshot) {
-          // We have to be regenerated if running from a snapshot.
-          throw const BuildScriptChangedException();
-        }
-
-        inputSources.removeAll(deletedSourceOutputs);
-        assetGraph = null;
-        buildScriptUpdates = null;
-        updates = null;
-        cleanBuild = true;
-      }
     }
 
     if (assetGraph == null) {
@@ -137,12 +118,6 @@ class _Loader {
         buildLog.error(e.toString());
         throw const CannotBuildException();
       }
-      buildScriptUpdates = await BuildScriptUpdates.create(
-        _environment.reader,
-        _options.packageGraph,
-        assetGraph,
-        disabled: _options.skipBuildScriptCheck,
-      );
 
       conflictingOutputs =
           assetGraph.outputs
@@ -171,21 +146,16 @@ class _Loader {
       await _initialBuildCleanup(conflictingOutputs, _environment.writer);
     }
 
-    return BuildDefinition._(
-      assetGraph,
-      buildScriptUpdates,
-      cleanBuild,
-      updates,
-    );
+    return BuildDefinition._(assetGraph, bootstrapper, cleanBuild, updates);
   }
 
   /// Deletes the generated output directory.
-  Future<void> _deleteGeneratedDir() async {
+  /*Future<void> _deleteGeneratedDir() async {
     var generatedDir = Directory(generatedOutputDirectory);
     if (await generatedDir.exists()) {
       await generatedDir.delete(recursive: true);
     }
-  }
+  }*/
 
   /// Returns which sources and builder options changed, and the [ChangeType]
   /// describing whether they where added, removed or modified.
@@ -220,5 +190,3 @@ class _Loader {
     await Future.wait(conflictingAssets.map((id) => writer.delete(id)));
   }
 }
-
-bool get _runningFromSnapshot => !Platform.script.path.endsWith('.dart');
diff --git a/build_runner_core/lib/src/generate/build_series.dart b/build_runner_core/lib/src/generate/build_series.dart
index 169240893..943bb429d 100644
--- a/build_runner_core/lib/src/generate/build_series.dart
+++ b/build_runner_core/lib/src/generate/build_series.dart
@@ -7,12 +7,13 @@ import 'dart:async';
 import 'package:build/build.dart';
 // ignore: implementation_imports
 import 'package:build/src/internal.dart';
+// ignore: implementation_imports
+import 'package:build_runner/src/internal.dart';
 import 'package:watcher/watcher.dart';
 
 import '../asset/finalized_reader.dart';
 import '../asset/writer.dart';
 import '../asset_graph/graph.dart';
-import '../changes/build_script_updates.dart';
 import '../environment/build_environment.dart';
 import '../logging/build_log.dart';
 import '../package_graph/apply_builders.dart';
@@ -39,7 +40,7 @@ import 'options.dart';
 class BuildSeries {
   final BuildEnvironment environment;
   final AssetGraph assetGraph;
-  final BuildScriptUpdates? buildScriptUpdates;
+  final Bootstrapper bootstrapper;
   final BuildOptions options;
   final BuildPhases buildPhases;
 
@@ -66,7 +67,7 @@ class BuildSeries {
   BuildSeries._(
     this.environment,
     this.assetGraph,
-    this.buildScriptUpdates,
+    this.bootstrapper,
     this.options,
     this.buildPhases,
     this.finalizedReader,
@@ -173,7 +174,7 @@ class BuildSeries {
     var build = BuildSeries._(
       environment,
       buildDefinition.assetGraph,
-      buildDefinition.buildScriptUpdates,
+      buildDefinition.bootstrapper,
       options,
       buildPhases,
       finalizedReader,
diff --git a/build_runner_core/lib/src/generate/options.dart b/build_runner_core/lib/src/generate/options.dart
index e7eb20d62..83e8b000e 100644
--- a/build_runner_core/lib/src/generate/options.dart
+++ b/build_runner_core/lib/src/generate/options.dart
@@ -121,9 +121,6 @@ class BuildOptions {
   /// Watch mode options.
   Duration debounceDelay;
 
-  /// For testing only, skips the build script updates check.
-  bool skipBuildScriptCheck;
-
   /// Listener for when builders report unused assets.
   void Function(AssetId, Iterable<AssetId>)? reportUnusedAssetsForInput;
 
@@ -131,7 +128,6 @@ class BuildOptions {
     required this.debounceDelay,
     required this.enableLowResourcesMode,
     required this.packageGraph,
-    required this.skipBuildScriptCheck,
     required this.trackPerformance,
     required this.targetGraph,
     required this.logPerformanceDir,
@@ -194,7 +190,6 @@ class BuildOptions {
       debounceDelay: debounceDelay,
       enableLowResourcesMode: enableLowResourcesMode,
       packageGraph: packageGraph,
-      skipBuildScriptCheck: skipBuildScriptCheck,
       trackPerformance: trackPerformance,
       targetGraph: targetGraph,
       logPerformanceDir: logPerformanceDir,
diff --git a/build_runner_core/test/changes/build_script_updates_test.dart b/build_runner_core/test/changes/build_script_updates_test.dart
index ecac172e0..9ba0c4597 100644
--- a/build_runner_core/test/changes/build_script_updates_test.dart
+++ b/build_runner_core/test/changes/build_script_updates_test.dart
@@ -1,8 +1,10 @@
+void main() {}
+
 // Copyright (c) 2023, 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';
+/*import 'package:build/build.dart';
 import 'package:build_runner_core/src/changes/build_script_updates.dart';
 import 'package:build_runner_core/src/package_graph/package_graph.dart';
 import 'package:package_config/package_config_types.dart';
@@ -75,3 +77,4 @@ void main() {
     });
   });
 }
+*/
diff --git a/build_runner_core/test/fixtures/workspace/.dart_tool/package_config.json b/build_runner_core/test/fixtures/workspace/.dart_tool/package_config.json
index e6174da4d..1823f7ffd 100644
--- a/build_runner_core/test/fixtures/workspace/.dart_tool/package_config.json
+++ b/build_runner_core/test/fixtures/workspace/.dart_tool/package_config.json
@@ -20,10 +20,9 @@
       "languageVersion": "3.7"
     }
   ],
-  "generated": "2025-03-06T13:52:35.390409Z",
   "generator": "pub",
-  "generatorVersion": "3.8.0-edge",
-  "flutterRoot": "file:///usr/local/google/home/davidmorgan/opt/flutter-sdk/flutter",
-  "flutterVersion": "3.29.0",
+  "generatorVersion": "3.9.0",
+  "flutterRoot": "file:///usr/local/google/home/davidmorgan/opt/flutter-sdk",
+  "flutterVersion": "3.35.1",
   "pubCache": "file:///usr/local/google/home/davidmorgan/.pub-cache"
 }