fix(mobile): check the current picker selection on a toggle

A second tap could reach Flutter before the rebuild that reflected the
first, and both toggles read the selection captured at build time, so the
same person was added twice. The diffed native table traps on a duplicate
row. Read the current selection instead, and fail loudly if a shown member
row is missing from the state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: studio <dc2fc481343672df31a689840c09299972e704dac592e0da6f18486646a7ee3e@buzz.block.builderlab.xyz>
Signed-off-by: Tom Brow <tomb@squareup.com>

mobile/ios/Runner/NativeAddMembersSheet.swift

@@ -296,7 +296,8 @@ final class NativeAddMembersViewController: UITableViewController, UISearchResul
     let changed = snapshot.itemIdentifiers.filter { item in
       drawn[item].map { $0 != next[item] } ?? false
     }
-    snapshot.reconfigureItems(changed.filter(previous.itemIdentifiers.contains))
+    let shown = Set(previous.itemIdentifiers)
+    snapshot.reconfigureItems(changed.filter(shown.contains))
     drawn = next
     let animate = view.window != nil && wasChosen != chosen.map(Item.member)
       && !UIAccessibility.isReduceMotionEnabled
@@ -327,7 +328,7 @@ final class NativeAddMembersViewController: UITableViewController, UISearchResul
     cell.contentView.accessibilityElementsHidden = false
     cell.isUserInteractionEnabled = !busy
     var content = UIListContentConfiguration.subtitleCell()
-    guard case .member(let pubkey) = item, let user = member(pubkey) else {
+    guard case .member(let pubkey) = item else {
       content.text = status
       content.textProperties.color = loadError && !atLimit ? Self.errorColor : .secondaryLabel
       content.textProperties.numberOfLines = 0
@@ -336,6 +337,7 @@ final class NativeAddMembersViewController: UITableViewController, UISearchResul
       cell.contentConfiguration = content
       return
     }
+    guard let user = member(pubkey) else { preconditionFailure("A shown member row must be in the state") }
     let chosen = selected.contains { $0["pubkey"] as? String == pubkey }
     let key = user["avatarKey"] as? String
     content.text = user["name"] as? String
@@ -378,10 +380,11 @@ final class NativeAddMembersViewController: UITableViewController, UISearchResul
   override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
     tableView.deselectRow(at: indexPath, animated: true)
     guard !busy, let item = rows.itemIdentifier(for: indexPath) else { return }
-    guard case .member(let pubkey) = item, let user = member(pubkey) else {
+    guard case .member(let pubkey) = item else {
       if loadError && !atLimit { send("retry", [:]) }
       return
     }
+    guard let user = member(pubkey) else { preconditionFailure("A shown member row must be in the state") }
     if user["unavailable"] as? Bool == true { return }
     send("toggle", ["pubkey": pubkey])
     // Where asked (New DM), a pick ends its query, as an inserted mention

mobile/lib/features/channels/add_members_sheet.dart

@@ -161,7 +161,11 @@ class AddChannelMembersSheet extends HookConsumerWidget {
     void toggleUser(MentionCandidate user) {
       if (isSubmitting.value) return;
       final normalized = user.pubkey.toLowerCase();
-      if (selectedPubkeys.contains(normalized)) {
+      // The current selection, not this build's: a second tap can land
+      // before the rebuild that reflects the first.
+      if (selectedUsers.value.any(
+        (selected) => selected.pubkey.toLowerCase() == normalized,
+      )) {
         selectedUsers.value = [
           for (final selected in selectedUsers.value)
             if (selected.pubkey.toLowerCase() != normalized) selected,

mobile/lib/features/channels/channels_page/sheets.dart

@@ -461,7 +461,9 @@ class _NewDirectMessageSheet extends HookConsumerWidget {
         },
         onToggle: (pubkey) {
           if (isSubmitting.value) return;
-          if (selectedPubkeys.contains(pubkey)) {
+          // The current selection, not this build's: a second tap can land
+          // before the rebuild that reflects the first.
+          if (selectedUsers.value.any((user) => user.pubkey == pubkey)) {
             selectedUsers.value = selectedUsers.value
                 .where((user) => user.pubkey != pubkey)
                 .toList();

mobile/test/features/channels/channels_page_test/native_creation_tests.dart

@@ -64,6 +64,22 @@ void registerNativeCreationTests(Widget Function(List<Override>) buildPage) {
       expect(found['detail'], isNull);
       await event('toggle', {'pubkey': _dmKey(2)});
       await event('query', {'value': 'Person'});
+      // Two taps before Flutter rebuilds still never list a person twice.
+      for (var tap = 0; tap < 2; tap++) {
+        await messenger.handlePlatformMessage(
+          bridge.name,
+          const StandardMethodCodec().encodeMethodCall(
+            MethodCall('toggle', {'session': session, 'pubkey': _dmKey(3)}),
+          ),
+          (_) {},
+        );
+      }
+      await tester.pumpAndSettle();
+      final picked = [
+        for (final user in states.last['selected'] as List)
+          (user as Map)['pubkey'],
+      ];
+      expect(picked.toSet(), hasLength(picked.length));
       for (final key in people.keys) {
         await event('toggle', {'pubkey': key});
       }