feat(#163): share a channel as a scannable QR (reference-app format)

Channel.toShareUri/fromShareUri/isValidShareUri encode the reference
MeshCore app's format: meshcore://channel/add?name=<url-encoded>&secret=<hex32>.
A "Share QR Code" action in the channel menu shows the QR via the existing
QrCodeShareDialog, so it round-trips with the reference app.

Encode/decode unit-tested against both real reference examples (#test, #echo).
Scan-to-add follows.

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

lib/l10n/app_en.arb

@@ -1982,6 +1982,16 @@
       }
     }
   },
+  "channels_shareQr": "Share QR Code",
+  "channels_shareQrTitle": "Share Channel",
+  "channels_shareQrInstructions": "Scan to add \"{name}\".",
+  "@channels_shareQrInstructions": {
+    "placeholders": {
+      "name": {
+        "type": "String"
+      }
+    }
+  },
   "community_hashtagPrivacyHint": "Community hashtag channels are only joinable by members of the community",
   "community_invalidQrCode": "Invalid community QR code",
   "community_alreadyMember": "Already a Member",

lib/l10n/app_localizations.dart

@@ -6356,6 +6356,24 @@ abstract class AppLocalizations {
   /// **'Scan this QR code to join \"{name}\"'**
   String community_qrInstructions(String name);
 
+  /// No description provided for @channels_shareQr.
+  ///
+  /// In en, this message translates to:
+  /// **'Share QR Code'**
+  String get channels_shareQr;
+
+  /// No description provided for @channels_shareQrTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Share Channel'**
+  String get channels_shareQrTitle;
+
+  /// No description provided for @channels_shareQrInstructions.
+  ///
+  /// In en, this message translates to:
+  /// **'Scan to add \"{name}\".'**
+  String channels_shareQrInstructions(String name);
+
   /// No description provided for @community_hashtagPrivacyHint.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_bg.dart

@@ -3677,6 +3677,17 @@ class AppLocalizationsBg extends AppLocalizations {
     return 'Сканирайте този QR код, за да се присъедините към $name.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Хаштаг каналите на общността са достъпни само за членове на общността';

lib/l10n/app_localizations_de.dart

@@ -3684,6 +3684,17 @@ class AppLocalizationsDe extends AppLocalizations {
     return 'Scannen Sie diesen QR-Code, um sich \"$name\" anzuschließen.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Community-Hashtag-Kanäle können nur von Mitgliedern der Community betreten werden';

lib/l10n/app_localizations_en.dart

@@ -3613,6 +3613,17 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Scan this QR code to join \"$name\"';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Community hashtag channels are only joinable by members of the community';

lib/l10n/app_localizations_es.dart

@@ -3672,6 +3672,17 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Escanear este código QR para unirte a $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Los canales de hashtag de la comunidad solo son accesibles para los miembros de la comunidad';

lib/l10n/app_localizations_fr.dart

@@ -3695,6 +3695,17 @@ class AppLocalizationsFr extends AppLocalizations {
     return 'Scanner ce QR code pour rejoindre $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Les canaux hashtag de la communauté ne sont accessibles qu\'aux membres de la communauté';

lib/l10n/app_localizations_hu.dart

@@ -3688,6 +3688,17 @@ class AppLocalizationsHu extends AppLocalizations {
     return 'Scanned this QR-kódot, hogy csatlakozhat a $name csoporthoz.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'A közösségi hashtagekhez tartozó csatornák csak a közösség tagjai számára érhetők el.';

lib/l10n/app_localizations_it.dart

@@ -3677,6 +3677,17 @@ class AppLocalizationsIt extends AppLocalizations {
     return 'Scansiona questo codice QR per unirti a $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'I canali hashtag della community sono accessibili solo ai membri della community';

lib/l10n/app_localizations_ja.dart

@@ -3490,6 +3490,17 @@ class AppLocalizationsJa extends AppLocalizations {
     return 'このQRコードをスキャンして、$nameに参加してください。';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'コミュニティハッシュタグのチャンネルは、コミュニティのメンバーのみが参加できます。';

lib/l10n/app_localizations_ko.dart

@@ -3492,6 +3492,17 @@ class AppLocalizationsKo extends AppLocalizations {
     return '이 QR 코드를 스캔하여 \"$name\"에 가입하세요.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       '커뮤니티 해시태그 채널은 커뮤니티 구성원만 가입할 수 있습니다.';

lib/l10n/app_localizations_nl.dart

@@ -3658,6 +3658,17 @@ class AppLocalizationsNl extends AppLocalizations {
     return 'Scan deze QR-code om je aan te sluiten bij $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Community hashtag-kanalen zijn alleen toegankelijk voor leden van de community';

lib/l10n/app_localizations_pl.dart

@@ -3690,6 +3690,17 @@ class AppLocalizationsPl extends AppLocalizations {
     return 'Skanuj ten kod QR, aby dołączyć $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Kanały hashtagowe społeczności są dostępne tylko dla członków społeczności';

lib/l10n/app_localizations_pt.dart

@@ -3671,6 +3671,17 @@ class AppLocalizationsPt extends AppLocalizations {
     return 'Escanear este código QR para juntar-se a $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Os canais de hashtag da comunidade só podem ser acessados por membros da comunidade';

lib/l10n/app_localizations_ru.dart

@@ -3679,6 +3679,17 @@ class AppLocalizationsRu extends AppLocalizations {
     return 'Отсканируйте этот QR-код, чтобы присоединиться к \"$name\"';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Хэштег-каналы сообщества доступны только его участникам';

lib/l10n/app_localizations_sk.dart

@@ -3657,6 +3657,17 @@ class AppLocalizationsSk extends AppLocalizations {
     return 'Skenejte tento QR kód, aby ste sa pripojili k $name.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Hashtagové kanály komunity sú prístupné len členom komunity';

lib/l10n/app_localizations_sl.dart

@@ -3652,6 +3652,17 @@ class AppLocalizationsSl extends AppLocalizations {
     return 'Skenirajte to QR kodo za vključitev $name.';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Hashtag kanali skupnosti so dostopni samo članom skupnosti';

lib/l10n/app_localizations_sv.dart

@@ -3632,6 +3632,17 @@ class AppLocalizationsSv extends AppLocalizations {
     return 'Skanna denna QR-kod för att gå med i \"$name\"';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Community-hashtagkanaler kan endast nås av medlemmar i communityn';

lib/l10n/app_localizations_uk.dart

@@ -3675,6 +3675,17 @@ class AppLocalizationsUk extends AppLocalizations {
     return 'Відскануйте цей QR-код, щоб приєднатись до $name';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint =>
       'Хештег-канали спільноти доступні лише членам спільноти';

lib/l10n/app_localizations_zh.dart

@@ -3395,6 +3395,17 @@ class AppLocalizationsZh extends AppLocalizations {
     return '扫描此二维码加入 \"$name\"';
   }
 
+  @override
+  String get channels_shareQr => 'Share QR Code';
+
+  @override
+  String get channels_shareQrTitle => 'Share Channel';
+
+  @override
+  String channels_shareQrInstructions(String name) {
+    return 'Scan to add \"$name\".';
+  }
+
   @override
   String get community_hashtagPrivacyHint => '仅社区成员可加入社区标签频道。';
 

lib/models/channel.dart

@@ -68,6 +68,32 @@ class Channel {
     return bytes;
   }
 
+  /// Reference-app channel share URI:
+  /// `meshcore://channel/add?name=<url-encoded>&secret=<32-hex PSK>`.
+  /// Round-trips with the reference MeshCore app's channel QR. (#161)
+  String toShareUri() =>
+      'meshcore://channel/add?name=${Uri.encodeComponent(name)}&secret=$pskHex';
+
+  /// Parses a channel from a reference-app share URI, or null if malformed.
+  /// [index] is the local slot the caller assigns on add. (#161)
+  static Channel? fromShareUri(String uri, {int index = 0}) {
+    final parsed = Uri.tryParse(uri.trim());
+    if (parsed == null || parsed.scheme != 'meshcore') return null;
+    if (parsed.host != 'channel') return null;
+    if (parsed.path.replaceAll('/', '') != 'add') return null;
+    final name = parsed.queryParameters['name'];
+    final secret = parsed.queryParameters['secret'];
+    if (name == null || secret == null) return null;
+    try {
+      return Channel(index: index, name: name, psk: parsePskHex(secret));
+    } catch (_) {
+      return null;
+    }
+  }
+
+  /// True if [uri] is a valid channel share URI. (#161)
+  static bool isValidShareUri(String uri) => fromShareUri(uri) != null;
+
   /// Derive PSK from hashtag name using SHA256.
   /// The hashtag is normalized to include '#' prefix.
   /// Returns first 16 bytes of SHA256 hash as PSK.

lib/screens/channels_screen.dart

@@ -519,6 +519,17 @@ class _ChannelsScreenState extends State<ChannelsScreen>
                 }
               },
             ),
+            ListTile(
+              leading: const Icon(Icons.qr_code_2),
+              title: Text(context.l10n.channels_shareQr),
+              onTap: () async {
+                Navigator.pop(sheetContext);
+                await Future.delayed(const Duration(milliseconds: 100));
+                if (parentContext.mounted) {
+                  _showChannelQrDialog(parentContext, channel);
+                }
+              },
+            ),
             ListTile(
               leading: Icon(
                 isMuted
@@ -1764,6 +1775,20 @@ class _ChannelsScreenState extends State<ChannelsScreen>
     );
   }
 
+  void _showChannelQrDialog(BuildContext context, Channel channel) {
+    QrCodeShareDialog.show(
+      context: context,
+      data: channel.toShareUri(),
+      title: context.l10n.channels_shareQrTitle,
+      instructions: context.l10n.channels_shareQrInstructions(channel.name),
+      embeddedImage: Image.asset(
+        'assets/images/mesh-icon.png',
+        width: 40,
+        height: 40,
+      ),
+    );
+  }
+
   void _confirmLeaveCommunity(BuildContext context, Community community) {
     final connector = context.read<MeshCoreConnector>();
 

test/models/channel_share_uri_test.dart

@@ -0,0 +1,62 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_open/models/channel.dart';
+
+void main() {
+  group('Channel share URI (#161)', () {
+    test('toShareUri matches the reference-app format', () {
+      final ch = Channel(
+        index: 0,
+        name: '#test',
+        psk: Channel.parsePskHex('9cd8fcf22a47333b591d96a2b848b73f'),
+      );
+      expect(
+        ch.toShareUri(),
+        'meshcore://channel/add?name=%23test&secret=9cd8fcf22a47333b591d96a2b848b73f',
+      );
+    });
+
+    test('fromShareUri parses a real reference example', () {
+      final ch = Channel.fromShareUri(
+        'meshcore://channel/add?name=%23echo&secret=5d25cf40b1f5b4a7eb0cf9703634a948',
+      );
+      expect(ch, isNotNull);
+      expect(ch!.name, '#echo');
+      expect(ch.pskHex, '5d25cf40b1f5b4a7eb0cf9703634a948');
+    });
+
+    test('round-trips name (incl. spaces) + psk', () {
+      final ch = Channel(
+        index: 3,
+        name: 'Private Ops',
+        psk: Channel.parsePskHex('0011223344556677889900aabbccddee'),
+      );
+      final back = Channel.fromShareUri(ch.toShareUri());
+      expect(back, isNotNull);
+      expect(back!.name, ch.name);
+      expect(back.pskHex, ch.pskHex);
+    });
+
+    test('rejects malformed / wrong-scheme URIs', () {
+      // wrong scheme
+      expect(
+        Channel.fromShareUri(
+          'https://channel/add?name=x&secret=9cd8fcf22a47333b591d96a2b848b73f',
+        ),
+        isNull,
+      );
+      // wrong host
+      expect(
+        Channel.fromShareUri('meshcore://contact/add?name=x&secret=00'),
+        isNull,
+      );
+      // missing secret
+      expect(Channel.fromShareUri('meshcore://channel/add?name=x'), isNull);
+      // secret not 16 bytes
+      expect(
+        Channel.fromShareUri('meshcore://channel/add?name=x&secret=abcd'),
+        isNull,
+      );
+      expect(Channel.isValidShareUri('not a uri at all'), isFalse);
+    });
+  });
+}