feat: breakout dynamic into flags/*

app_dart/lib/src/request_handlers/scheduler/batch_backfiller.dart

@@ -63,7 +63,7 @@ final class BatchBackfiller extends RequestHandler {
       }
       final fsGrid = await _firestore.queryRecentCommitsAndTasks(
         slug,
-        commitLimit: config.backfillerCommitLimit,
+        commitLimit: config.flags.backfillerCommitLimit,
         branch: branch.reference,
       );
       await _doBackfillFrom(slug, fsGrid);
@@ -74,7 +74,7 @@ final class BatchBackfiller extends RequestHandler {
     log.debug('Running default branch backfiller for "$slug"');
     final fsGrid = await _firestore.queryRecentCommitsAndTasks(
       slug,
-      commitLimit: config.backfillerCommitLimit,
+      commitLimit: config.flags.backfillerCommitLimit,
       branch: Config.defaultBranch(slug),
     );
     return await _doBackfillFrom(slug, fsGrid);

app_dart/lib/src/request_handlers/scheduler/vacuum_stale_tasks.dart

@@ -69,7 +69,7 @@ final class VacuumStaleTasks extends RequestHandler {
 
     final recentCommits = await _firestore.queryRecentCommitsAndTasks(
       slug,
-      commitLimit: config.backfillerCommitLimit,
+      commitLimit: config.flags.backfillerCommitLimit,
       status: TaskStatus.inProgress,
       branch: branch,
     );

app_dart/lib/src/service/config.dart

@@ -20,6 +20,7 @@ import 'package:yaml/yaml.dart' show YamlMap, loadYaml;
 import '../../cocoon_service.dart';
 import '../foundation/providers.dart' show Providers;
 import '../foundation/typedefs.dart' show HttpClientProvider;
+import 'flags/content_aware_hashing_flags.dart';
 import 'github_service.dart';
 import 'luci_build_service/cipd_version.dart';
 
@@ -33,6 +34,9 @@ interface class Config {
   Config(this._cache, this._secrets, {required DynamicConfig dynamicConfig})
     : _dynamicConfig = dynamicConfig;
 
+  /// Access dynamically configured flags.
+  DynamicConfig get flags => _dynamicConfig;
+
   /// When present on a pull request, instructs Cocoon to submit it
   /// automatically as soon as all the required checks pass.
   ///
@@ -211,12 +215,6 @@ interface class Config {
   /// the next API call.
   int get backfillerTargetLimit => 75;
 
-  /// Upper limit of commit rows to be backfilled in API call.
-  ///
-  /// This limits the number of commits to be checked to backfill. When bots
-  /// are idle, we hope to scan as many commit rows as possible.
-  int get backfillerCommitLimit => _dynamicConfig.backfillerCommitLimit;
-
   /// Upper limit of issue/PRs allowed each API call.
   ///
   /// GitHub enforces a secondary rate limit on frequency API calls. This causes
@@ -504,7 +502,7 @@ interface class Config {
 ///
 /// Should be read from git/HEAD/app_dart/config.yaml and cached between
 /// services.
-@JsonSerializable()
+@JsonSerializable(explicitToJson: true)
 @immutable
 final class DynamicConfig {
   /// Upper limit of commit rows to be backfilled in API call.
@@ -514,12 +512,17 @@ final class DynamicConfig {
   @JsonKey(defaultValue: 50)
   final int backfillerCommitLimit;
 
-  DynamicConfig({required this.backfillerCommitLimit});
+  final ContentAwareHashingJson contentAwareHashing;
+
+  DynamicConfig({
+    required this.backfillerCommitLimit,
+    required this.contentAwareHashing,
+  });
 
   /// Connect the generated [_$DynamicConfigFromJson] function to the `fromJson`
   /// factory.
-  factory DynamicConfig.fromJson(Map<String, Object?> json) =>
-      _$DynamicConfigFromJson(json);
+  factory DynamicConfig.fromJson(Map<String, Object?>? json) =>
+      _$DynamicConfigFromJson(json ?? {});
 
   /// Connect the generated [_$DynamicConfigToJson] function to the `toJson` method.
   Map<String, dynamic> toJson() => _$DynamicConfigToJson(this);

app_dart/lib/src/service/flags/content_aware_hashing_flags.dart

@@ -0,0 +1,26 @@
+// Copyright 2025 The Flutter Authors. 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:json_annotation/json_annotation.dart';
+import 'package:meta/meta.dart';
+
+part 'content_aware_hashing_flags.g.dart';
+
+@JsonSerializable()
+@immutable
+final class ContentAwareHashingJson {
+  ContentAwareHashingJson({required this.waitOnContentHash});
+
+  /// Merge Groups should wait for the content hash before scheduling.
+  @JsonKey(defaultValue: false)
+  final bool waitOnContentHash;
+
+  /// Connect the generated [_$ContentAwareHashingJsonFromJson] function to the `fromJson`
+  /// factory.
+  factory ContentAwareHashingJson.fromJson(Map<String, Object?>? json) =>
+      _$ContentAwareHashingJsonFromJson(json ?? {});
+
+  /// Connect the generated [_$ContentAwareHashingJsonToJson] function to the `toJson` method.
+  Map<String, dynamic> toJson() => _$ContentAwareHashingJsonToJson(this);
+}

app_dart/test/request_handlers/scheduler/batch_backfiller_test.dart

@@ -48,9 +48,9 @@ void main() {
     mockGithubChecksUtil = MockGithubChecksUtil();
     firestore = FakeFirestoreService();
     config = FakeConfig(
-      backfillerCommitLimitValue: 10,
       backfillerTargetLimitValue: 100,
       supportedReposValue: {Config.flutterSlug},
+      dynamicConfig: DynamicConfig.fromJson({'backfillerCommitLimit': 10}),
     );
     ciYamlFetcher = FakeCiYamlFetcher();
 
@@ -100,7 +100,7 @@ void main() {
   }) async {
     final grid = await firestore.queryRecentCommitsAndTasks(
       Config.flutterSlug,
-      commitLimit: commits ?? config.backfillerCommitLimit,
+      commitLimit: commits ?? config.flags.backfillerCommitLimit,
       branch: branch,
     );
 
@@ -270,7 +270,7 @@ void main() {
   });
 
   test('only considers the top X commits', () async {
-    config.backfillerCommitLimitValue = 1;
+    config.dynamicConfig = DynamicConfig.fromJson({'backfillerCommitLimit': 1});
 
     // dart format off
     await fillStorageAndSetCiYaml([

app_dart/test/service/dynamic_config_updater_test.dart

@@ -129,7 +129,7 @@ void main() {
       '${requestUris.last}',
       'https://raw.githubusercontent.com/flutter/cocoon/main/app_dart/config.yaml',
     );
-    expect(config.backfillerCommitLimit, 100);
+    expect(config.flags.backfillerCommitLimit, 100);
   });
 }
 

app_dart/test/src/fake_config.dart

@@ -49,11 +49,11 @@ class FakeConfig implements Config {
     this.supportedReposValue,
     this.batchSizeValue,
     this.backfillerTargetLimitValue,
-    this.backfillerCommitLimitValue,
     this.issueAndPRLimitValue,
     this.githubRequestDelayValue,
     DynamicConfig? dynamicConfig,
-  });
+  }) : dynamicConfig =
+           dynamicConfig ?? DynamicConfig.fromJson(<String, Object?>{});
 
   gh.GitHub? githubClient;
   GraphQLClient? githubGraphQLClient;
@@ -75,7 +75,6 @@ class FakeConfig implements Config {
   String? releaseCandidateBranchPathValue;
   Set<String>? rollerAccountsValue;
   int? backfillerTargetLimitValue;
-  int? backfillerCommitLimitValue;
   int? issueAndPRLimitValue;
   String? flutterGoldPendingValue;
   String? flutterGoldSuccessValue;
@@ -89,6 +88,7 @@ class FakeConfig implements Config {
   Set<gh.RepositorySlug>? supportedReposValue;
   Set<gh.RepositorySlug>? postsubmitSupportedReposValue;
   Duration? githubRequestDelayValue;
+  DynamicConfig dynamicConfig;
 
   @override
   Future<gh.GitHub> createGitHubClient({
@@ -120,9 +120,6 @@ class FakeConfig implements Config {
   @override
   int get backfillerTargetLimit => backfillerTargetLimitValue ?? 50;
 
-  @override
-  int get backfillerCommitLimit => backfillerCommitLimitValue ?? 50;
-
   @override
   int get issueAndPRLimit => issueAndPRLimitValue ?? 2;
 
@@ -268,4 +265,8 @@ class FakeConfig implements Config {
   @override
   Future<String> get discordTreeStatusWebhookUrl async =>
       'https://discord.com/api/webhooks/1234/abcd';
+
+  @override
+  // TODO: implement flags
+  DynamicConfig get flags => dynamicConfig;
 }