176990 Implement get presubmit guard api

app_dart/lib/server.dart

@@ -7,6 +7,7 @@ import 'dart:math';
 
 import 'cocoon_service.dart';
 import 'src/request_handlers/get_engine_artifacts_ready.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';
@@ -155,6 +156,39 @@ 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/update-suppressed-test': UpdateSuppressedTest(
       authenticationProvider: authProvider,
       firestore: firestore,

app_dart/lib/src/model/ci_yaml/target.dart

@@ -338,9 +338,6 @@ class Dependency {
   final String? version;
 
   Map<String, Object> toJson() {
-    return <String, Object>{
-      'dependency': name,
-      if (version != null) 'version': version!,
-    };
+    return <String, Object>{'dependency': name, 'version': ?version};
   }
 }

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

@@ -150,9 +150,9 @@ abstract class AppDocument<T extends AppDocument<T>> implements g.Document {
     // Copied from [g.Document.toJson].
     return {
       'fields': fields,
-      if (createTime != null) 'createTime': createTime!,
-      if (name != null) 'name': name!,
-      if (updateTime != null) 'updateTime': updateTime!,
+      'createTime': ?createTime,
+      'name': ?name,
+      'updateTime': ?updateTime,
     };
   }
 

app_dart/lib/src/request_handlers/get_presubmit_guard.dart

@@ -0,0 +1,81 @@
+// 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 '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';
+
+@immutable
+final class GetPresubmitGuard extends ApiRequestHandler {
+  const GetPresubmitGuard({
+    required super.config,
+    required super.authenticationProvider,
+    required FirestoreService firestore,
+  }) : _firestore = firestore;
+
+  final FirestoreService _firestore;
+
+  static const String kSlugParam = 'slug';
+  static const String kShaParam = 'sha';
+
+  @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(null);
+    }
+
+    // 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: [
+        ...guards.map(
+          (g) => rpc_model.PresubmitGuardStage(
+            name: g.stage.name,
+            createdAt: g.creationTime,
+            builds: g.builds,
+          ),
+        ),
+      ],
+    );
+
+    return Response.json(response.toJson());
+  }
+}

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';
 
@@ -101,7 +102,7 @@ mixin FirestoreQueries {
     created ??= TimeRange.indefinite;
     final filterMap = <String, Object>{
       '${Commit.fieldRepositoryPath} =': slug.fullName,
-      if (branch != null) '${Commit.fieldBranch} =': branch,
+      '${Commit.fieldBranch} =': ?branch,
       ..._filterByTimeRange(Commit.fieldCreateTimestamp, created),
     };
     final orderMap = <String, String>{
@@ -124,9 +125,9 @@ mixin FirestoreQueries {
     Transaction? transaction,
   }) async {
     final filterMap = {
-      if (name != null) '${Task.fieldName} =': name,
+      '${Task.fieldName} =': ?name,
       if (status != null) '${Task.fieldStatus} =': status.value,
-      if (commitSha != null) '${Task.fieldCommitSha} =': commitSha,
+      '${Task.fieldCommitSha} =': ?commitSha,
     };
 
     // Avoid a full table-scan.

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/lib/src/service/luci_build_service.dart

@@ -668,9 +668,7 @@ class LuciBuildService {
       log.info(
         'create postsubmit schedule request for target: ${pending.target} in commit ${commit.sha}',
       );
-      final properties = <String, Object>{
-        if (contentHash != null) 'content_hash': contentHash,
-      };
+      final properties = <String, Object>{'content_hash': ?contentHash};
       final scheduleBuildRequest = await _createPostsubmitScheduleBuild(
         commit: commit,
         target: pending.target,
@@ -736,9 +734,7 @@ class LuciBuildService {
         'create postsubmit schedule request for target: $target in commit ${commit.sha}',
       );
 
-      final properties = <String, Object>{
-        if (contentHash != null) 'content_hash': contentHash,
-      };
+      final properties = <String, Object>{'content_hash': ?contentHash};
       final scheduleBuildRequest = await _createMergeGroupScheduleBuild(
         commit: commit,
         target: target,

app_dart/lib/src/service/scheduler/ci_yaml_fetcher.dart

@@ -122,10 +122,7 @@ interface class CiYamlFetcher {
     // If totCiYaml is not null, we assume the caller has verified that the
     // current branch is not a release branch.
     return CiYamlSet(
-      yamls: {
-        CiType.any: rootConfig,
-        if (engineConfig != null) CiType.fusionEngine: engineConfig,
-      },
+      yamls: {CiType.any: rootConfig, CiType.fusionEngine: ?engineConfig},
       slug: commit.slug,
       branch: commit.branch,
       totConfig: totCiYaml,