fix: Fix the demo app when migrations mismatch (#93)

example/offline_sync_demo/lib/src/demo_controller.dart

@@ -1011,9 +1011,10 @@ class DemoController extends ChangeNotifier {
     if (!dbDir.existsSync()) {
       dbDir.createSync(recursive: true);
     }
-    final replica = await OfflineReplica.open(
+    final databasePath = p.join(dbDir.path, '${user.username}-${slot.name}.db');
+    final replica = await OfflineReplica.openOrReset(
       client: client,
-      databasePath: p.join(dbDir.path, '${user.username}-${slot.name}.db'),
+      databasePath: databasePath,
       persistentUserId: user.authUserId,
     );
     _sessions[key] = replica;

example/offline_sync_demo/lib/src/offline_replica.dart

@@ -1,4 +1,7 @@
-import 'package:flutter/foundation.dart' show kDebugMode;
+import 'dart:io';
+
+import 'package:flutter/foundation.dart' show debugPrint, kDebugMode;
+import 'package:path/path.dart' as p;
 import 'package:serverpod_database/serverpod_database.dart'
     show ClientDatabaseSession;
 import 'package:serverpod_offline_sync_client/serverpod_offline_sync_client.dart';
@@ -13,8 +16,10 @@ import 'table_ops.dart' show demoSyncTables;
 /// understand the package. The four steps are:
 ///
 ///   1. [open] opens a local SQLite database ([Client.createSession])
-///      and wraps it in a [CrdtDatabaseSession]. The rest of the app
-///      reads and writes generated models through [session].
+///      and wraps it in a [CrdtDatabaseSession]. Use
+///      [openOrReset] when the file may predate the shipped
+///      schema. The rest of the app reads and writes generated models through
+///      [session].
 ///   2. CRUD happens against [session] with the generated model APIs (see
 ///      the `seed*` methods in `DemoController` for the plain, recommended form,
 ///      e.g. `Person.db.insertRow(crdtSession, person)`).
@@ -63,6 +68,41 @@ class OfflineReplica {
     return OfflineReplica._(rawSession, crdtSession, persistentUserId);
   }
 
+  /// Like [open], but deletes [databasePath] and retries once when opening
+  /// fails — for example when migrations were regenerated during development
+  /// and a leftover file records a version this build no longer ships.
+  ///
+  /// A replica is a disposable local cache; syncing re-pulls server state.
+  static Future<OfflineReplica> openOrReset({
+    required Client client,
+    required String databasePath,
+    required UuidValue persistentUserId,
+  }) async {
+    var retry = true;
+    while (true) {
+      try {
+        return await open(
+          client: client,
+          databasePath: databasePath,
+          persistentUserId: persistentUserId,
+        );
+      } catch (_) {
+        if (!retry) rethrow;
+        retry = false;
+        for (final suffix in const ['', '-wal', '-shm']) {
+          final file = File('$databasePath$suffix');
+          if (file.existsSync()) file.deleteSync();
+        }
+        if (kDebugMode) {
+          debugPrint(
+            'offline_sync_demo: discarded stale replica '
+            '${p.basename(databasePath)}.',
+          );
+        }
+      }
+    }
+  }
+
   /// Pushes local pending changes through [client] and merges remote ones once.
   ///
   /// Connectivity is expressed entirely by [client]: pass an online client to

example/offline_sync_demo/lib/src/table_ops.dart

@@ -178,6 +178,10 @@ final Map<String, TableOps> demoTableOps = {
       create: (id, label, foreignKeys) =>
           UniqueComposite(id: id, scope: label, value: label),
     ),
+    _ops<UniqueDiscriminator>(
+      create: (id, label, foreignKeys) =>
+          UniqueDiscriminator(id: id, categoryId: 0, name: label),
+    ),
     _ops<UniqueSetNullChild>(
       create: (id, label, foreignKeys) => UniqueSetNullChild(
         id: id,