fix(mobile): recover historical namesake chip identity

Signed-off-by: Logan Johnson <loganj@squareup.com>

mobile/lib/shared/mentions/mention_bindings.dart

@@ -90,23 +90,25 @@ Map<String, Set<String>> renderedMentionBindings(
       key: key,
     ));
     add(label, key);
+    bindings.putIfAbsent(match.group(1)!.toLowerCase(), () => <String>{});
   }
   final winning = mentionOccurrences(
     content,
     bindings.keys,
   ).map((range) => range.label).toSet();
-  for (final entry in bindings.entries) {
-    if (entry.value.length < 2) continue;
-    entry.value.removeAll(
-      qualified
-          .where(
-            (q) =>
-                q.base == entry.key &&
-                winning.contains(q.label) &&
-                bindings[q.label]?.length == 1,
-          )
-          .map((q) => q.key),
-    );
+  final claimed = qualified.where((q) => winning.contains(q.label)).toList();
+  final bases = claimed.map((q) => q.base).where(winning.contains).toSet();
+  final remaining = keys.difference(claimed.map((q) => q.key).toSet());
+  // Ordinary sibling mentions claim their own identities before recovering a
+  // historical namesake. Current aliases must not retarget that namesake.
+  for (final label in winning.difference(bases)) {
+    final candidates = bindings[label]!;
+    if (candidates.length == 1) remaining.removeAll(candidates);
+  }
+  for (final base in bases) {
+    // Multiple historical labels or leftover tagged keys cannot be paired
+    // deterministically. Leave them as non-clickable references, not guesses.
+    bindings[base] = bases.length == 1 ? remaining.toSet() : <String>{};
   }
   return bindings;
 }

mobile/test/features/channels/message_content_exact_mentions_test.dart

@@ -67,4 +67,46 @@ void main() {
     expect(tester.takeException(), isNull);
     semantics.dispose();
   });
+  testWidgets('historical namesakes preserve targets with ordinary siblings', (
+    tester,
+  ) async {
+    final first = 'a' * 64, second = 'b' * 64, sibling = 'c' * 64;
+    for (final firstName in ['Scout', 'Renamed Scout', first]) {
+      for (final secondName in ['Scout', 'Renamed Scout', second]) {
+        for (final reverse in [false, true]) {
+          for (final ambiguous in [false, true]) {
+            final entries = {
+              first: firstName,
+              second: secondName,
+              sibling: 'Alice',
+              if (ambiguous) 'd' * 64: 'Unknown',
+            }.entries.toList();
+            String? tapped;
+            await tester.pumpWidget(
+              WidgetHelpers.testable(
+                child: MessageContent(
+                  content: '@Scout @Scout ($second) @Alice',
+                  mentionNames: Map.fromEntries(
+                    reverse ? entries.reversed : entries,
+                  ),
+                  onMentionTap: (key) => tapped = key,
+                ),
+              ),
+            );
+            await tester.pumpAndSettle();
+            if (ambiguous) {
+              expect(find.text(firstName), findsNothing);
+            } else {
+              await tester.tap(find.text(firstName));
+              expect(tapped, first);
+            }
+            await tester.tap(find.text('Scout (bbbbbbbb…bbbb)'));
+            expect(tapped, second);
+            await tester.tap(find.text('Alice'));
+            expect(tapped, sibling);
+          }
+        }
+      }
+    }
+  });
 }