feat: do not set "unknown sender for this chat" error

deltachat-ffi/deltachat.h

@@ -7214,6 +7214,8 @@ void dc_event_unref(dc_event_t* event);
 /// "Unknown sender for this chat. See 'info' for more details."
 ///
 /// Use as message text if assigning the message to a chat is not totally correct.
+///
+/// @deprecated 2025-08-18
 #define DC_STR_UNKNOWN_SENDER_FOR_CHAT    72
 
 /// "Message from %1$s"

src/receive_imf.rs

@@ -1693,12 +1693,6 @@ async fn add_parts(
             let name: &str = from.display_name.as_ref().unwrap_or(&from.addr);
             for part in &mut mime_parser.parts {
                 part.param.set(Param::OverrideSenderDisplayname, name);
-
-                if chat.is_protected() {
-                    // In protected chat, also mark the message with an error.
-                    let s = stock_str::unknown_sender_for_chat(context).await;
-                    part.error = Some(s);
-                }
             }
         }
     }

src/securejoin/securejoin_tests.rs

@@ -634,7 +634,7 @@ async fn test_unknown_sender() -> Result<()> {
     // The message from Bob is delivered late, Bob is already removed.
     let msg = alice.recv_msg(&sent).await;
     assert_eq!(msg.text, "Hi hi!");
-    assert_eq!(msg.error.unwrap(), "Unknown sender for this chat.");
+    assert_eq!(msg.get_override_sender_name().unwrap(), "bob@example.net");
 
     Ok(())
 }

src/stock_str.rs

@@ -123,9 +123,6 @@ pub enum StockMessage {
                     however, of course, if they like, you may point them to 👉 https://get.delta.chat"))]
     WelcomeMessage = 71,
 
-    #[strum(props(fallback = "Unknown sender for this chat."))]
-    UnknownSenderForChat = 72,
-
     #[strum(props(fallback = "Message from %1$s"))]
     SubjectForNewContact = 73,
 
@@ -909,11 +906,6 @@ pub(crate) async fn welcome_message(context: &Context) -> String {
     translated(context, StockMessage::WelcomeMessage).await
 }
 
-/// Stock string: `Unknown sender for this chat.`.
-pub(crate) async fn unknown_sender_for_chat(context: &Context) -> String {
-    translated(context, StockMessage::UnknownSenderForChat).await
-}
-
 /// Stock string: `Message from %1$s`.
 // TODO: This can compute `self_name` itself instead of asking the caller to do this.
 pub(crate) async fn subject_for_new_contact(context: &Context, self_name: &str) -> String {