fix: Keep tombstones for two days before deleting (#3685)

This is a way to prevent redownloading locally deleted messages. Otherwise if a message is deleted
quickly after sending and `bcc_self` is configured, the BCC copy is downloaded and appears as a new
message as it happens for messages sent from another device.

python/tests/test_0_complex_or_slow.py

@@ -1,4 +1,5 @@
 import sys
+import time
 
 import pytest
 import deltachat as dc
@@ -675,3 +676,16 @@ def test_verified_group_vs_delete_server_after(acfactory, tmp_path, lp):
     assert msg_in.chat == chat2_offl
     assert msg_in.get_sender_contact().addr == ac2.get_config("addr")
     assert ac2_offl_ac1_contact.is_verified()
+
+
+def test_deleted_msgs_dont_reappear(acfactory):
+    ac1 = acfactory.new_online_configuring_account()
+    acfactory.bring_accounts_online()
+    ac1.set_config("bcc_self", "1")
+    chat = ac1.get_self_contact().create_chat()
+    msg = chat.send_text("hello")
+    ac1._evtracker.get_matching("DC_EVENT_SMTP_MESSAGE_SENT")
+    ac1.delete_messages([msg])
+    ac1._evtracker.get_matching("DC_EVENT_MSG_DELETED")
+    time.sleep(5)
+    assert len(chat.get_messages()) == 0

src/sql.rs

@@ -990,16 +990,19 @@ async fn maybe_add_from_param(
     Ok(())
 }
 
-/// Removes from the database locally deleted messages that also don't
+/// Removes from the database stale locally deleted messages that also don't
 /// have a server UID.
 async fn prune_tombstones(sql: &Sql) -> Result<()> {
+    // Keep tombstones for the last two days to prevent redownloading locally deleted messages.
+    let timestamp_max = time().saturating_sub(2 * 24 * 3600);
     sql.execute(
         "DELETE FROM msgs
          WHERE chat_id=?
+         AND timestamp<=?
          AND NOT EXISTS (
          SELECT * FROM imap WHERE msgs.rfc724_mid=rfc724_mid AND target!=''
          )",
-        (DC_CHAT_ID_TRASH,),
+        (DC_CHAT_ID_TRASH, timestamp_max),
     )
     .await?;
     Ok(())