176990 Implement get presubmit guard api

app_dart/lib/server.dart

@@ -8,6 +8,7 @@ import 'dart:math';
 import 'cocoon_service.dart';
 import 'src/request_handlers/get_engine_artifacts_ready.dart';
 import 'src/request_handlers/get_presubmit_checks.dart';
+import 'src/request_handlers/get_presubmit_guard.dart';
 import 'src/request_handlers/get_tree_status_changes.dart';
 import 'src/request_handlers/github_webhook_replay.dart';
 import 'src/request_handlers/lookup_hash.dart';
@@ -156,8 +157,42 @@ Server createServer({
       authenticationProvider: authProvider,
       firestore: firestore,
     ),
+
+    /// Returns the presubmit guard status for a given slug and commit SHA.
+    ///
+    /// Consolidates multiple [PresubmitGuard] records (one per stage) into a single response.
+    ///
+    /// GET: /api/get-presubmit-guard
+    ///
+    /// Parameters:
+    ///   slug: (string in query) required. The repository owner/name (e.g., 'flutter/flutter').
+    ///   sha: (string in query) required. The commit SHA to query for.
+    ///
+    /// Response: Status 200 OK
+    /// Returns [PresubmitGuardResponse]:
+    ///  {
+    ///    "pr_num": 123,
+    ///    "check_run_id": 456,
+    ///    "author": "dash",
+    ///    "stages": [
+    ///      {
+    ///        "name": "fusion",
+    ///        "created_at": 123456789,
+    ///        "builds": {
+    ///          "test1": "Succeeded",
+    ///          "test2": "In Progress"
+    ///        }
+    ///      }
+    ///    ]
+    ///  }
+    '/api/get-presubmit-guard': GetPresubmitGuard(
+      config: config,
+      authenticationProvider: authProvider,
+      firestore: firestore,
+    ),
     '/api/get-presubmit-checks': GetPresubmitChecks(
       config: config,
+      authenticationProvider: authProvider,
       firestore: firestore,
     ),
     '/api/update-suppressed-test': UpdateSuppressedTest(

app_dart/lib/src/request_handlers/get_presubmit_checks.dart

@@ -8,6 +8,7 @@ import 'dart:io';
 import 'package:cocoon_common/rpc_model.dart';
 
 import '../../cocoon_service.dart';
+import '../request_handling/api_request_handler.dart';
 import '../service/firestore/unified_check_run.dart';
 
 /// Returns all checks for a specific presubmit check run.
@@ -30,9 +31,10 @@ import '../service/firestore/unified_check_run.dart';
 ///     "summary": "Check passed"
 ///   }
 /// ]
-final class GetPresubmitChecks extends RequestHandler {
+final class GetPresubmitChecks extends ApiRequestHandler {
   const GetPresubmitChecks({
     required super.config,
+    required super.authenticationProvider,
     required FirestoreService firestore,
   }) : _firestore = firestore;
 

app_dart/lib/src/request_handlers/get_presubmit_guard.dart

@@ -0,0 +1,96 @@
+// 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:async';
+import 'dart:io';
+
+import 'package:cocoon_common/guard_status.dart';
+import 'package:cocoon_common/rpc_model.dart' as rpc_model;
+import 'package:github/github.dart';
+import 'package:meta/meta.dart';
+
+import '../../cocoon_service.dart';
+import '../request_handling/api_request_handler.dart';
+import '../service/firestore/unified_check_run.dart';
+
+/// Request handler for retrieving the aggregated presubmit guard status.
+///
+/// This handler queries the presubmit guards for a specific commit SHA and
+/// returns an aggregated response including the overall guard status and
+/// individual stage statuses.
+@immutable
+final class GetPresubmitGuard extends ApiRequestHandler {
+  /// Defines the [GetPresubmitGuard] handler.
+  const GetPresubmitGuard({
+    required super.config,
+    required super.authenticationProvider,
+    required FirestoreService firestore,
+  }) : _firestore = firestore;
+
+  final FirestoreService _firestore;
+
+  /// The name of the query parameter for the repository slug (e.g. 'flutter/flutter').
+  static const String kSlugParam = 'slug';
+
+  /// The name of the query parameter for the commit SHA.
+  static const String kShaParam = 'sha';
+
+  /// Handles the HTTP GET request.
+  ///
+  /// Requires [kSlugParam] and [kShaParam] query parameters.
+  /// Returns a JSON response with the aggregated presubmit guard data.
+  @override
+  Future<Response> get(Request request) async {
+    checkRequiredQueryParameters(request, [kSlugParam, kShaParam]);
+
+    final slugName = request.uri.queryParameters[kSlugParam]!;
+    final sha = request.uri.queryParameters[kShaParam]!;
+
+    final slug = RepositorySlug.full(slugName);
+    final guards = await UnifiedCheckRun.getPresubmitGuardsForCommitSha(
+      firestoreService: _firestore,
+      slug: slug,
+      commitSha: sha,
+    );
+
+    if (guards.isEmpty) {
+      return Response.json({
+        'error': 'No guard found for slug $slug and sha $sha',
+      }, statusCode: HttpStatus.notFound);
+    }
+
+    // Consolidate metadata from the first record.
+    final first = guards.first;
+
+    final GuardStatus guardStatus;
+    if (guards.any((g) => g.failedBuilds > 0)) {
+      guardStatus = GuardStatus.failed;
+    } else if (guards.every(
+      (g) => g.failedBuilds == 0 && g.remainingBuilds == 0,
+    )) {
+      guardStatus = GuardStatus.succeeded;
+    } else if (guards.every((g) => g.remainingBuilds == g.builds.length)) {
+      guardStatus = GuardStatus.waitingForBackfill;
+    } else {
+      guardStatus = GuardStatus.inProgress;
+    }
+
+    final response = rpc_model.PresubmitGuardResponse(
+      prNum: first.pullRequestId,
+      checkRunId: first.checkRunId,
+      author: first.author,
+      guardStatus: guardStatus,
+      stages: [
+        for (final g in guards)
+          rpc_model.PresubmitGuardStage(
+            name: g.stage.name,
+            createdAt: g.creationTime,
+            builds: g.builds,
+          ),
+      ],
+    );
+
+    return Response.json(response);
+  }
+}

app_dart/lib/src/service/firestore.dart

@@ -16,6 +16,7 @@ import '../../cocoon_service.dart';
 import '../model/firestore/commit.dart';
 import '../model/firestore/github_build_status.dart';
 import '../model/firestore/github_gold_status.dart';
+
 import '../model/firestore/task.dart';
 import 'firestore/commit_and_tasks.dart';
 

app_dart/lib/src/service/firestore/unified_check_run.dart

@@ -230,6 +230,19 @@ final class UnifiedCheckRun {
     )).firstOrNull;
   }
 
+  /// Queries for [PresubmitGuard] records by [slug] and [commitSha].
+  static Future<List<PresubmitGuard>> getPresubmitGuardsForCommitSha({
+    required FirestoreService firestoreService,
+    required RepositorySlug slug,
+    required String commitSha,
+  }) async {
+    return await _queryPresubmitGuards(
+      firestoreService: firestoreService,
+      slug: slug,
+      commitSha: commitSha,
+    );
+  }
+
   static Future<List<PresubmitGuard>> _queryPresubmitGuards({
     required FirestoreService firestoreService,
     Transaction? transaction,
@@ -246,10 +259,10 @@ final class UnifiedCheckRun {
     int? limit,
   }) async {
     final filterMap = {
-      '${PresubmitGuard.fieldSlug} =': ?slug,
+      '${PresubmitGuard.fieldSlug} =': ?slug?.fullName,
       '${PresubmitGuard.fieldPullRequestId} =': ?pullRequestId,
       '${PresubmitGuard.fieldCheckRunId} =': ?checkRunId,
-      '${PresubmitGuard.fieldStage} =': ?stage,
+      '${PresubmitGuard.fieldStage} =': ?stage?.name,
       '${PresubmitGuard.fieldCreationTime} =': ?creationTime,
       '${PresubmitGuard.fieldAuthor} =': ?author,
       '${PresubmitGuard.fieldCommitSha} =': ?commitSha,

app_dart/test/request_handlers/get_presubmit_checks_test.dart

@@ -14,6 +14,7 @@ import 'package:cocoon_service/src/request_handlers/get_presubmit_checks.dart';
 import 'package:test/test.dart';
 
 import '../src/fake_config.dart';
+import '../src/request_handling/fake_dashboard_authentication.dart';
 import '../src/request_handling/fake_http.dart';
 import '../src/request_handling/request_handler_tester.dart';
 import '../src/service/fake_firestore_service.dart';
@@ -30,7 +31,11 @@ void main() {
       config = FakeConfig();
       tester = RequestHandlerTester();
       firestoreService = FakeFirestoreService();
-      handler = GetPresubmitChecks(config: config, firestore: firestoreService);
+      handler = GetPresubmitChecks(
+        config: config,
+        firestore: firestoreService,
+        authenticationProvider: FakeDashboardAuthentication(),
+      );
     });
 
     Future<List<PresubmitCheckResponse>?> getPresubmitCheckResponse(