Fix media placeholders and image cache

server/QMax.Api/Controllers/ChatsController.cs

@@ -106,6 +106,7 @@ public sealed class ChatsController(
         }
 
         var messages = (await query.ToArrayAsync(cancellationToken))
+            .Where(message => !IsGenericPreviewPlaceholder(message))
             .OrderByDescending(x => x.SentAt)
             .Take(Math.Clamp(take, 1, 200))
             .ToArray();
@@ -121,6 +122,11 @@ public sealed class ChatsController(
             return;
         }
 
+        if (MessageTextSanitizer.IsGenericMediaLabel(preview))
+        {
+            return;
+        }
+
         var previewAt = chat.LastMessageAt.Value;
         if (chat.HistoryClearedAt is { } historyClearedAt && previewAt <= historyClearedAt)
         {
@@ -202,6 +208,14 @@ public sealed class ChatsController(
         return hash.ToString("x8");
     }
 
+    private static bool IsGenericPreviewPlaceholder(Message message)
+    {
+        return message.Direction == MessageDirection.Incoming &&
+            message.Attachments.Count == 0 &&
+            message.ExternalId?.StartsWith("preview:", StringComparison.Ordinal) == true &&
+            MessageTextSanitizer.IsGenericMediaLabel(message.Text);
+    }
+
     [HttpPost("{chatId:guid}/read")]
     public async Task<IActionResult> MarkRead(Guid chatId, CancellationToken cancellationToken)
     {