fix(firestore): read old_value for delete events in onDocumentDeleted handler

lib/src/firestore/firestore_namespace.dart

@@ -452,7 +452,12 @@ class FirestoreNamespace extends FunctionsNamespace {
           final params = _extractParams(document, headers.documentPath);
 
           final parsed = await _parseBody(request);
-          final snapshot = parsed?['value'];
+          final snapshotKey =
+              (methodName == 'onDocumentDeleted' ||
+                  methodName == 'onDocumentDeletedWithAuthContext')
+              ? 'old_value'
+              : 'value';
+          final snapshot = parsed?[snapshotKey];
 
           try {
             if (withAuthContext) {

test/e2e/tests/firestore_tests.dart

@@ -98,13 +98,39 @@ void runFirestoreTests(
       await client.deleteDocument('users/$testUserId');
       print('✓ Document deleted successfully');
 
-      // Wait for trigger
+      // Wait for trigger to fire and write result
       await Future<void>.delayed(const Duration(seconds: 2));
 
       // Verify document no longer exists
       final doc = await client.getDocument('users/$testUserId');
       expect(doc, isNull, reason: 'Document should not exist after deletion');
       print('✓ Document deletion verified');
+
+      // Poll for the side-channel result doc written by the handler
+      // (up to 5 attempts × 500ms = 2.5s extra headroom)
+      Map<String, dynamic>? result;
+      for (var i = 0; i < 5; i++) {
+        result = await client.getDocument(
+          'trigger_results/deleted_$testUserId',
+        );
+        if (result != null) break;
+        await Future<void>.delayed(const Duration(milliseconds: 500));
+      }
+
+      expect(
+        result,
+        isNotNull,
+        reason: 'trigger_results doc should have been written by handler',
+      );
+      expect(
+        result!['fields']['hasData']['booleanValue'],
+        isTrue,
+        reason: 'event.data should be non-null for delete events',
+      );
+      expect(result['fields']['name']['stringValue'], 'To Be Deleted');
+      expect(result['fields']['email']['stringValue'], 'delete@example.com');
+      expect(result['fields']['finalMessage']['stringValue'], 'goodbye');
+      print('✓ Handler received correct pre-deletion document data');
     });
 
     test('onDocumentWritten fires for all operations', () async {
@@ -283,6 +309,12 @@ void runFirestoreTests(
       } catch (e) {
         // Ignore errors during cleanup
       }
+      // Clean up side-channel result doc written by the onDocumentDeleted handler
+      try {
+        await client.deleteDocument('trigger_results/deleted_$testUserId');
+      } catch (e) {
+        // Ignore errors during cleanup
+      }
     });
   });
 }

test/fixtures/dart_reference/lib/main.dart

@@ -1,3 +1,6 @@
+import 'dart:convert';
+import 'dart:io';
+
 import 'package:firebase_functions/firebase_functions.dart';
 
 // =============================================================================
@@ -184,6 +187,43 @@ void main(List<String> args) async {
       final data = event.data?.data();
       print('Document deleted: users/${event.params['userId']}');
       print('  Final data: $data');
+
+      // write result to Firestore so the e2e test can assert on
+      // what the handler actually received (exposes the old_value/value).
+      final userId = event.params['userId'] as String;
+      final firestoreHost =
+          Platform.environment['FIRESTORE_EMULATOR_HOST'] ?? '127.0.0.1:8080';
+      final parts = firestoreHost.split(':');
+      final host = parts[0];
+      final port = int.tryParse(parts.length > 1 ? parts[1] : '8080') ?? 8080;
+
+      final resultFields = <String, dynamic>{
+        'hasData': {'booleanValue': data != null},
+        'name': {'stringValue': data?['name']?.toString() ?? ''},
+        'email': {'stringValue': data?['email']?.toString() ?? ''},
+        'finalMessage': {
+          'stringValue': data?['finalMessage']?.toString() ?? '',
+        },
+      };
+
+      try {
+        final httpClient = HttpClient();
+        final req = await httpClient.post(
+          host,
+          port,
+          '/v1/projects/demo-test/databases/(default)/documents/'
+          'trigger_results?documentId=deleted_$userId',
+        );
+        req.headers.contentType = ContentType.json;
+        req.write(jsonEncode({'fields': resultFields}));
+        await req.close();
+        httpClient.close();
+      } catch (e) {
+        print(
+          '  Firestore write to verify handler '
+          'received event.data failed: $e',
+        );
+      }
     });
 
     firebase.firestore.onDocumentWritten(document: 'users/{userId}', (