Sync DM chat name/icon on user changes

Add a signal to keep direct-message chat name and icon in sync when a user updates their username or avatar, and register it in AppConfig.ready. Also initialize a DM chat's name/icon on creation from the other member's username/avatar if those fields are missing, saving only the changed fields.

backend/social/chat/apps.py

@@ -6,3 +6,6 @@ class ChatConfig(AppConfig):
     name = 'social.chat'
 
     label = "chat"
+
+    def ready(self):
+        import social.chat.signals  # noqa: F401

backend/social/chat/signals.py

@@ -0,0 +1,35 @@
+from django.conf import settings
+from django.db.models.signals import post_save
+from django.dispatch import receiver
+
+
+@receiver(post_save, sender=settings.AUTH_USER_MODEL)
+def sync_dm_chat_identity(sender, instance, created, update_fields, **kwargs):
+    """Keep DM chat name/icon in sync when a user updates their username or avatar."""
+    if created:
+        return
+
+    changed = set(update_fields) if update_fields else None  # None = full save
+    username_changed = changed is None or 'username' in changed
+    avatar_changed = changed is None or 'avatar' in changed
+
+    if not (username_changed or avatar_changed):
+        return
+
+    from .models import Chat
+
+    dm_chats = Chat.objects.filter(
+        chat_type=Chat.ChatType.DM,
+        members=instance,
+    ).exclude(owner=instance)
+
+    if not dm_chats.exists():
+        return
+
+    update_kwargs = {}
+    if username_changed:
+        update_kwargs['name'] = instance.username
+    if avatar_changed:
+        update_kwargs['icon'] = instance.avatar.name if instance.avatar else None
+
+    dm_chats.update(**update_kwargs)

backend/social/chat/views.py

@@ -53,7 +53,19 @@ class ChatViewSet(viewsets.ModelViewSet):
         return Chat.objects.filter(Q(members=user) | Q(owner=user)).distinct()
 
     def perform_create(self, serializer):
-        serializer.save(owner=self.request.user)
+        chat = serializer.save(owner=self.request.user)
+        if chat.chat_type == Chat.ChatType.DM:
+            other = chat.members.exclude(pk=self.request.user.pk).first()
+            if other:
+                update_fields = []
+                if not chat.name:
+                    chat.name = other.username
+                    update_fields.append('name')
+                if not chat.icon and other.avatar:
+                    chat.icon = other.avatar
+                    update_fields.append('icon')
+                if update_fields:
+                    chat.save(update_fields=update_fields)
 
     # ------------------------------------------------------------------
     # Member management