fix: stop cross-folder message_id dedup — mails were being moved between folders

- message_id dedup was searching across ALL folders
- A mail in Trash with same message_id as one in INBOX was found and moved to INBOX
- Now message_id dedup only searches within the SAME folder
- This matches how real mail clients work: same message_id in different folders = separate copies

app/plugins/builtins/mail/services.py

@@ -636,7 +636,9 @@ async def imap_sync_folder(
                 )
             ).scalar_one_or_none()
 
-            # Also check by message_id — mail may have been moved to Trash by IMAP server
+            # Also check by message_id — but ONLY within the same folder
+            # to prevent cross-folder moves. A mail in Trash and INBOX with
+            # the same message_id are separate copies (like real mail clients).
             if not existing_mail:
                 # Fetch headers first to get Message-ID
                 fetch_hdr = await client.uid('fetch', uid_str, '(BODY.PEEK[HEADER.FIELDS (MESSAGE-ID)])')
@@ -655,6 +657,7 @@ async def imap_sync_folder(
                                     and_(
                                         Mail.account_id == account.id,
                                         Mail.message_id == peek_msg_id,
+                                        Mail.folder_id == folder.id,
                                         Mail.tenant_id == tenant_id,
                                     )
                                 )
@@ -1163,6 +1166,7 @@ async def imap_sync_account(
                                     and_(
                                         Mail.account_id == account.id,
                                         Mail.message_id == message_id,
+                                        Mail.folder_id == folder.id,
                                         Mail.tenant_id == tenant_id,
                                     )
                                 )