feat(firestore): add support for Pipeline APIs

packages/cloud_firestore/cloud_firestore/lib/cloud_firestore.dart

@@ -53,7 +53,16 @@ part 'src/filters.dart';
 part 'src/firestore.dart';
 part 'src/load_bundle_task.dart';
 part 'src/load_bundle_task_snapshot.dart';
+part 'pipeline_snapshot.dart';
 part 'src/persistent_cache_index_manager.dart';
+part 'src/pipeline.dart';
+part 'src/pipeline_aggregate.dart';
+part 'src/pipeline_distance.dart';
+part 'src/pipeline_expression.dart';
+part 'src/pipeline_ordering.dart';
+part 'src/pipeline_sample.dart';
+part 'src/pipeline_source.dart';
+part 'src/pipeline_stage.dart';
 part 'src/query.dart';
 part 'src/query_document_snapshot.dart';
 part 'src/query_snapshot.dart';

packages/cloud_firestore/cloud_firestore/lib/pipeline_snapshot.dart

@@ -0,0 +1,26 @@
+// Copyright 2026, the Chromium 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.
+
+part of 'cloud_firestore.dart';
+
+/// Result of executing a pipeline
+class PipelineResult {
+  final DocumentReference<Map<String, dynamic>> document;
+  final DateTime createTime;
+  final DateTime updateTime;
+
+  PipelineResult({
+    required this.document,
+    required this.createTime,
+    required this.updateTime,
+  });
+}
+
+/// Snapshot containing pipeline execution results
+class PipelineSnapshot {
+  final List<PipelineResult> result;
+  final DateTime executionTime;
+
+  PipelineSnapshot._(this.result, this.executionTime);
+}

packages/cloud_firestore/cloud_firestore/lib/src/firestore.dart

@@ -339,6 +339,25 @@ class FirebaseFirestore extends FirebasePluginPlatform {
     return null;
   }
 
+  /// Returns a [PipelineSource] for creating and executing pipelines.
+  ///
+  /// Pipelines allow you to perform complex queries and transformations on
+  /// Firestore data using a fluent API.
+  ///
+  /// Example:
+  /// ```dart
+  /// final snapshot = await FirebaseFirestore.instance
+  ///     .pipeline()
+  ///     .collection('users')
+  ///     .where(PipelineFilter(Field('age'), isGreaterThan: 18))
+  ///     .sort(Field('name').ascending())
+  ///     .limit(10)
+  ///     .execute();
+  /// ```
+  PipelineSource pipeline() {
+    return PipelineSource._(this);
+  }
+
   /// Configures indexing for local query execution. Any previous index configuration is overridden.
   ///
   /// The index entries themselves are created asynchronously. You can continue to use queries that