feat: move dashboard's dev_cocoon to integration tests (#4961)

Updates the dashboard code to use a "real" server in the browser.
Currently, `DevelopmentCocoonService` in
`dashboard/lib/service/dev_cocoon.dart` generates fake data manually.
While effective, it doesn't test end-to-end with the backend logic or
API surface, leading to a false sense of security (and having caused
multiple 'push to prod to fix'). By using `IntegrationServer`, we can
run the real `app_dart` logic against in-memory fakes (Firestore,
BigQuery, etc.), ensuring the frontend is tested against the same logic
the production server uses.

1. defangs app_dart/lib/** by removing app_engine and dart:io.
    * gae_server.dart passes in the needed "dart:io" handlers
* server.dart now handles an abstract Request, which can be real (app
engine, local server) or fake (tests / dashboard local).
* "dynamic config" no longer looks up the config.yaml from the read only
filesystem and instead we build dynamic config with build hooks -
`generated_config.dart`.
2. Removes dev_cocoon and its hardcoded mockery (partial reason for the
image diffs)
3. Adds `IntegrationServerAdapter` (which is an
`AppEngineCocoonService`) to wrap and make fake http calls to the
`IntegrationServer`.

Author: jtmcdole

app_dart/analysis_options.yaml

@@ -1,5 +1,10 @@
 include: ../analysis_options.yaml
 
+analyzer:
+  exclude:
+    # Optional: exclude the generated file if you don't want it analyzed
+    - hook/build.dart
+
 linter:
   rules:
     # a few rules listed below are the ones we would like to exclude from flutter_lint package, for app_dart

app_dart/bin/gae_server.dart

@@ -11,6 +11,7 @@ import 'package:cocoon_service/cocoon_service.dart';
 import 'package:cocoon_service/server.dart';
 import 'package:cocoon_service/src/foundation/appengine_utils.dart';
 import 'package:cocoon_service/src/foundation/providers.dart';
+import 'package:cocoon_service/src/request_handling/http_io.dart';
 import 'package:cocoon_service/src/service/big_query.dart';
 import 'package:cocoon_service/src/service/build_status_service.dart';
 import 'package:cocoon_service/src/service/commit_service.dart';
@@ -143,7 +144,9 @@ Future<void> main() async {
     );
 
     return runAppEngine(
-      server,
+      (HttpRequest request) async {
+        await server(request.toRequest());
+      },
       onAcceptingConnections: (InternetAddress address, int port) {
         final host = address.isLoopback ? 'localhost' : address.host;
         print('Serving requests at http://$host:$port/');

app_dart/hook/build.dart

@@ -0,0 +1,32 @@
+// Copyright 2026 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 'dart:io';
+
+import 'package:native_assets_cli/native_assets_cli.dart';
+
+void main(List<String> args) async {
+  await build(args, (config, output) async {
+    // 1. Read the source file (e.g., your App Engine config)
+    final configFile = File('config.yaml');
+    final content = await configFile.readAsString();
+
+    // 2. Define the path for the generated code
+    // It's best to put this in 'lib/src/generated_config.dart'
+    final outputFile = File('lib/src/generated_config.dart');
+
+    // 3. Write the file as a raw string constant
+    await outputFile.writeAsString("""
+// GENERATED CODE - DO NOT MODIFY BY HAND
+// Generated by build.dart hook
+
+const String configFileContent =
+    r\'\'\'$content\'\'\';
+""");
+
+    // 4. (Optional) Tell Dart that this hook depends on the config file
+    // This ensures that if config.yaml changes, the hook runs again.
+    output.addDependency(configFile.uri);
+  });
+}

app_dart/lib/cocoon_service.dart

@@ -4,6 +4,13 @@
 
 export 'src/foundation/context.dart';
 export 'src/foundation/utils.dart';
+export 'src/model/firestore/base.dart' hide AppDocument;
+export 'src/model/firestore/commit.dart';
+export 'src/model/firestore/presubmit_check.dart';
+export 'src/model/firestore/presubmit_guard.dart';
+export 'src/model/firestore/suppressed_test.dart';
+export 'src/model/firestore/task.dart';
+export 'src/model/firestore/tree_status_change.dart';
 export 'src/request_handlers/check_flaky_builders.dart';
 export 'src/request_handlers/create_branch.dart';
 export 'src/request_handlers/dart_internal_subscription.dart';
@@ -35,6 +42,7 @@ export 'src/request_handling/authentication.dart';
 export 'src/request_handling/cache_request_handler.dart';
 export 'src/request_handling/checkrun_authentication.dart';
 export 'src/request_handling/dashboard_authentication.dart';
+export 'src/request_handling/http_utils.dart';
 export 'src/request_handling/pubsub.dart';
 export 'src/request_handling/pubsub_authentication.dart';
 export 'src/request_handling/request_handler.dart';
@@ -47,6 +55,7 @@ export 'src/service/build_bucket_client.dart';
 export 'src/service/cache_service.dart';
 export 'src/service/config.dart';
 export 'src/service/firestore.dart';
+export 'src/service/flags/dynamic_config.dart';
 export 'src/service/gerrit_service.dart';
 export 'src/service/github_checks_service.dart';
 export 'src/service/luci_build_service.dart';

app_dart/lib/server.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:io';
 import 'dart:math';
 
 import 'cocoon_service.dart';
@@ -25,7 +24,7 @@ import 'src/service/content_aware_hash_service.dart';
 import 'src/service/discord_service.dart';
 import 'src/service/scheduler/ci_yaml_fetcher.dart';
 
-typedef Server = Future<void> Function(HttpRequest);
+typedef Server = Future<void> Function(Request);
 
 /// Creates a service with the given dependencies.
 Server createServer({
@@ -404,7 +403,7 @@ Server createServer({
     '/readiness_check': ReadinessCheck(config: config),
   };
 
-  return (HttpRequest request) async {
+  return (Request request) async {
     if (handlers.containsKey(request.uri.path)) {
       final handler = handlers[request.uri.path]!;
       await handler.service(request);

app_dart/lib/src/foundation/github_checks_util.dart

@@ -3,13 +3,13 @@
 // found in the LICENSE file.
 
 import 'dart:core';
-import 'dart:io';
 
 import 'package:cocoon_server/logging.dart';
 import 'package:github/github.dart' as github;
 import 'package:github/hooks.dart';
 import 'package:retry/retry.dart';
 
+import '../request_handling/http_utils.dart';
 import '../service/config.dart';
 
 /// Wrapper class for github checkrun service. This is used to simplify

app_dart/lib/src/foundation/utils.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:cocoon_server/logging.dart';
 import 'package:github/github.dart';

app_dart/lib/src/generated_config.dart

@@ -2,11 +2,10 @@
 // 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:googleapis/firestore/v1.dart' as g;
 import 'package:path/path.dart' as p;
 
+import '../../request_handling/http_utils.dart';
 import '../../service/firestore.dart';
 import 'base.dart';
 

app_dart/lib/src/model/firestore/account.dart

@@ -5,15 +5,12 @@
 /// @docImport 'task.dart';
 library;
 
-import 'dart:io';
-
 import 'package:github/github.dart';
 import 'package:googleapis/firestore/v1.dart' hide Status;
 import 'package:path/path.dart' as p;
 import 'package:truncate/truncate.dart';
 
 import '../../../cocoon_service.dart';
-import '../../service/firestore.dart';
 import '../commit_ref.dart';
 import 'base.dart';