add a device message when backup transfer ends

that way, UI can just close the transfer dialog,
so that, at the end, both devices end in the chatlist.

we can also use this for troubleshooting -
if the device message is not present,
transfer did not succeed completely.

(a separate device message may be nice in that case -
but that is another effort,
same for making the device message reappear after deletion
or after some time)

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## 1.112.6 - unreleased
 
+### Changes
+
+- Add a device message after backup transfer #4301
+
 ### Fixed
 
 - Updated `iroh` from 0.4.0 to 0.4.1 to fix transfer of large accounts with many blob files.

deltachat-ffi/deltachat.h

@@ -7069,6 +7069,11 @@ void dc_event_unref(dc_event_t* event);
 /// `%1$s` will be replaced by name and address of the account.
 #define DC_STR_BACKUP_TRANSFER_QR 162
 
+/// "Account transferred to your second device."
+///
+/// Used as a device message after a successful backup transfer.
+#define DC_STR_BACKUP_TRANSFER_MSG_BODY 163
+
 /**
  * @}
  */

src/imex/transfer.rs

@@ -47,9 +47,11 @@ use tokio_stream::wrappers::ReadDirStream;
 use tokio_util::sync::CancellationToken;
 
 use crate::blob::BlobDirContents;
-use crate::chat::delete_and_reset_all_device_msgs;
+use crate::chat::{add_device_msg, delete_and_reset_all_device_msgs};
 use crate::context::Context;
+use crate::message::{Message, Viewtype};
 use crate::qr::Qr;
+use crate::stock_str::backup_transfer_msg_body;
 use crate::{e2ee, EventType};
 
 use super::{export_database, DBFILE_BACKUP_NAME};
@@ -270,7 +272,12 @@ impl BackupProvider {
             }
         };
         match &res {
-            Ok(_) => context.emit_event(SendProgress::Completed.into()),
+            Ok(_) => {
+                context.emit_event(SendProgress::Completed.into());
+                let mut msg = Message::new(Viewtype::Text);
+                msg.text = Some(backup_transfer_msg_body(context).await);
+                add_device_msg(context, None, Some(&mut msg)).await?;
+            }
             Err(err) => {
                 error!(context, "Backup transfer failure: {err:#}");
                 context.emit_event(SendProgress::Failed.into())

src/stock_str.rs

@@ -407,6 +407,9 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "Scan to set up second device for %1$s"))]
     BackupTransferQr = 162,
+
+    #[strum(props(fallback = "ℹ️ Account transferred to your second device."))]
+    BackupTransferMsgBody = 163,
 }
 
 impl StockMessage {
@@ -1261,6 +1264,10 @@ pub(crate) async fn backup_transfer_qr(context: &Context) -> Result<String> {
         .replace1(&full_name))
 }
 
+pub(crate) async fn backup_transfer_msg_body(context: &Context) -> String {
+    translated(context, StockMessage::BackupTransferMsgBody).await
+}
+
 impl Context {
     /// Set the stock string for the [StockMessage].
     ///