fix(mobile): tag kind:5 deletions with channel id

Mobile's deleteMessage emitted a kind:5 deletion with only an `e` tag,
so other clients' h-scoped channel subscriptions never observed the
delete until a non-channel-scoped fetch backfilled it. Mirror desktop's
build_delete_compat: emit both `['h', channelId]` and `['e', eventId]`.

Threads channelId through ChannelActions.deleteMessage and its callers.
Tag construction is extracted to buildDeleteMessageTags for testing.

Signed-off-by: Taylor Ho <taylorkmho@gmail.com>

Author: tellaho

mobile/lib/features/channels/channel_management_provider.dart

@@ -214,6 +214,19 @@ final channelCanvasProvider = FutureProvider.family<ChannelCanvas, String>((
   );
 });
 
+/// Channel-scoped kind:5 deletion tags. The `h` tag lets channel-scoped
+/// subscriptions observe the delete; the `e` tag points at the target event.
+@visibleForTesting
+List<List<String>> buildDeleteMessageTags({
+  required String channelId,
+  required String eventId,
+}) {
+  return [
+    ['h', channelId],
+    ['e', eventId],
+  ];
+}
+
 class ChannelActions {
   final Ref _ref;
   final RelaySessionNotifier _session;
@@ -438,13 +451,14 @@ class ChannelActions {
     );
   }
 
-  Future<void> deleteMessage(String eventId) async {
+  Future<void> deleteMessage({
+    required String channelId,
+    required String eventId,
+  }) async {
     await _signedEventRelay.submit(
       kind: EventKind.deletion,
       content: '',
-      tags: [
-        ['e', eventId],
-      ],
+      tags: buildDeleteMessageTags(channelId: channelId, eventId: eventId),
     );
   }
 

mobile/lib/features/channels/message_actions.dart

@@ -160,6 +160,7 @@ void showMessageActions({
                   _confirmDelete(
                     context: context,
                     ref: ref,
+                    channelId: channelId,
                     messageId: message.id,
                   );
                 },
@@ -242,6 +243,7 @@ void _showEditSheet({
 void _confirmDelete({
   required BuildContext context,
   required WidgetRef ref,
+  required String channelId,
   required String messageId,
 }) {
   showDialog<void>(
@@ -257,7 +259,10 @@ void _confirmDelete({
         FilledButton(
           onPressed: () {
             Navigator.of(dialogContext).pop();
-            ref.read(channelActionsProvider).deleteMessage(messageId);
+            ref.read(channelActionsProvider).deleteMessage(
+              channelId: channelId,
+              eventId: messageId,
+            );
           },
           style: FilledButton.styleFrom(
             backgroundColor: Theme.of(dialogContext).colorScheme.error,

mobile/lib/features/forum/forum_provider.dart

@@ -132,7 +132,7 @@ Future<void> deleteForumEvent(
   String? rootEventId,
 }) async {
   final actions = ref.read(channelActionsProvider);
-  await actions.deleteMessage(eventId);
+  await actions.deleteMessage(channelId: channelId, eventId: eventId);
   ref.invalidate(forumPostsProvider(channelId));
   if (rootEventId != null) {
     ref.invalidate(

mobile/test/features/channels/channel_management_provider_test.dart

@@ -84,4 +84,18 @@ void main() {
     expect(details.ttlDeadline, isNotNull);
     expect(details.ttlDeadline!.isUtc, isTrue);
   });
+
+  group('buildDeleteMessageTags', () {
+    test('emits both channel h tag and target e tag', () {
+      final tags = buildDeleteMessageTags(
+        channelId: 'c8c629ae-d35c-44fa-bc39-f6c1816756cc',
+        eventId: 'abc123',
+      );
+
+      expect(tags, [
+        ['h', 'c8c629ae-d35c-44fa-bc39-f6c1816756cc'],
+        ['e', 'abc123'],
+      ]);
+    });
+  });
 }