Fix MAX emoji attachments

server/QMax.Api/Program.cs

@@ -160,9 +160,12 @@ static async Task EnsureCompatibilitySchemaAsync(QMaxDbContext db)
         await db.Database.ExecuteSqlRawAsync("ALTER TABLE MessageAttachments ADD COLUMN ExternalId TEXT;");
     }
 
+    await RemoveDuplicateMessageAttachmentsAsync(db);
+    await db.Database.ExecuteSqlRawAsync("DROP INDEX IF EXISTS IX_MessageAttachments_MessageId_ExternalId;");
     await db.Database.ExecuteSqlRawAsync("""
-        CREATE INDEX IF NOT EXISTS IX_MessageAttachments_MessageId_ExternalId
-        ON MessageAttachments (MessageId, ExternalId);
+        CREATE UNIQUE INDEX IF NOT EXISTS IX_MessageAttachments_MessageId_ExternalId
+        ON MessageAttachments (MessageId, ExternalId)
+        WHERE ExternalId IS NOT NULL AND ExternalId <> '';
         """);
 
     await db.Database.ExecuteSqlRawAsync("""
@@ -189,6 +192,29 @@ static async Task EnsureCompatibilitySchemaAsync(QMaxDbContext db)
     await RemoveGenericMediaLabelsAsync(db);
 }
 
+static async Task RemoveDuplicateMessageAttachmentsAsync(QMaxDbContext db)
+{
+    var attachments = await db.MessageAttachments
+        .Where(attachment => attachment.ExternalId != null && attachment.ExternalId != "")
+        .ToListAsync();
+
+    var duplicates = attachments
+        .OrderBy(attachment => attachment.MessageId)
+        .ThenBy(attachment => attachment.ExternalId)
+        .ThenByDescending(attachment => attachment.FileSizeBytes)
+        .ThenBy(attachment => attachment.CreatedAt)
+        .GroupBy(attachment => new { attachment.MessageId, attachment.ExternalId })
+        .SelectMany(group => group.Skip(1))
+        .ToList();
+    if (duplicates.Count == 0)
+    {
+        return;
+    }
+
+    db.MessageAttachments.RemoveRange(duplicates);
+    await db.SaveChangesAsync();
+}
+
 static async Task RemoveGenericMediaLabelsAsync(QMaxDbContext db)
 {
     var placeholderMessages = await db.Messages