feat(#829): per-channel region-scope store (Epic #815 C1)

ChannelRegionScopeStore persists a channel-index -> region-name map per device (first 10 hex of the device key, matching the other channel stores). set/clear/scopeFor, null = unscoped. Tests cover round-trip, per-device and per-channel isolation, persistence, and no-device-key guard.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/storage/channel_region_scope_store.dart

@@ -0,0 +1,39 @@
+import '../utils/app_logger.dart';
+import 'prefs_manager.dart';
+
+/// Per-channel region scope, persisted per device (Feature #812, Epic #815).
+///
+/// Stores the region name a channel's outgoing messages should ride, keyed by
+/// the first 10 hex chars of the connected device's public key (the same
+/// scoping the other channel stores use). The name is the `#`-stripped region
+/// name from discovery; null/absent means the channel is unscoped.
+class ChannelRegionScopeStore {
+  static const String _keyPrefix = 'channel_region_scope_';
+
+  String publicKeyHex = '';
+  set setPublicKeyHex(String value) =>
+      publicKeyHex = value.length > 10 ? value.substring(0, 10) : '';
+
+  String _key(int channelIndex) => '$_keyPrefix${publicKeyHex}_$channelIndex';
+
+  /// The region name scoping [channelIndex], or null when unscoped.
+  Future<String?> scopeFor(int channelIndex) async {
+    if (publicKeyHex.isEmpty) return null;
+    return PrefsManager.instance.getString(_key(channelIndex));
+  }
+
+  /// Scope [channelIndex] to [regionName].
+  Future<void> setScope(int channelIndex, String regionName) async {
+    if (publicKeyHex.isEmpty) {
+      appLogger.warn('No device key set; cannot save channel region scope.');
+      return;
+    }
+    await PrefsManager.instance.setString(_key(channelIndex), regionName);
+  }
+
+  /// Remove the region scope on [channelIndex] (back to unscoped).
+  Future<void> clearScope(int channelIndex) async {
+    if (publicKeyHex.isEmpty) return;
+    await PrefsManager.instance.remove(_key(channelIndex));
+  }
+}

test/storage/channel_region_scope_store_test.dart

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+// Epic #815 T C1: per-channel region-scope store.
+// Device-key scoped (first 10 hex chars of the device public key), channel -> region name.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_open/storage/channel_region_scope_store.dart';
+import 'package:meshcore_open/storage/prefs_manager.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+const _devA = 'aabbccddee0011223344';
+const _devB = 'ffeeddccbb0011223344';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  setUp(() async {
+    SharedPreferences.setMockInitialValues({});
+    PrefsManager.reset();
+    await PrefsManager.initialize();
+  });
+
+  ChannelRegionScopeStore storeFor(String deviceKeyHex) {
+    final s = ChannelRegionScopeStore();
+    s.setPublicKeyHex = deviceKeyHex;
+    return s;
+  }
+
+  test('set / get / clear round-trip', () async {
+    final store = storeFor(_devA);
+    expect(await store.scopeFor(0), isNull);
+    await store.setScope(0, 'oki');
+    expect(await store.scopeFor(0), 'oki');
+    await store.clearScope(0);
+    expect(await store.scopeFor(0), isNull);
+  });
+
+  test('scopes are isolated per device key', () async {
+    await storeFor(_devA).setScope(2, 'oki');
+    expect(await storeFor(_devB).scopeFor(2), isNull);
+    expect(await storeFor(_devA).scopeFor(2), 'oki');
+  });
+
+  test('scopes are isolated per channel index', () async {
+    final store = storeFor(_devA);
+    await store.setScope(1, 'oki');
+    expect(await store.scopeFor(3), isNull);
+    expect(await store.scopeFor(1), 'oki');
+  });
+
+  test('survives a fresh store instance (persisted to prefs)', () async {
+    await storeFor(_devA).setScope(5, 'test');
+    final reopened = storeFor(_devA);
+    expect(await reopened.scopeFor(5), 'test');
+  });
+
+  test('with no device key set, reads null and writes are refused', () async {
+    final store = ChannelRegionScopeStore();
+    await store.setScope(0, 'oki');
+    expect(await store.scopeFor(0), isNull);
+  });
+}