refactor(timeline): retry_event_decryption: re-use utd cause

Rather than calling `UtdCause::determine` again when an event is successfully
decrypted on retry, re-use the cause we already determined.

crates/matrix-sdk-ui/src/timeline/controller/mod.rs

@@ -989,8 +989,6 @@ impl<P: RoomDataProvider> TimelineController<P> {
         decryptor: impl Decryptor,
         session_ids: Option<BTreeSet<String>>,
     ) {
-        use matrix_sdk::crypto::types::events::UtdCause;
-
         use super::EncryptedMessage;
 
         let mut state = self.state.clone().write_owned().await;
@@ -1038,16 +1036,17 @@ impl<P: RoomDataProvider> TimelineController<P> {
                 async move {
                     let event_item = item.as_event()?;
 
-                    let session_id = match event_item.content().as_unable_to_decrypt()? {
-                        EncryptedMessage::MegolmV1AesSha2 { session_id, .. }
-                            if should_retry(session_id) =>
-                        {
-                            session_id
-                        }
-                        EncryptedMessage::MegolmV1AesSha2 { .. }
-                        | EncryptedMessage::OlmV1Curve25519AesSha2 { .. }
-                        | EncryptedMessage::Unknown => return None,
-                    };
+                    let (session_id, utd_cause) =
+                        match event_item.content().as_unable_to_decrypt()? {
+                            EncryptedMessage::MegolmV1AesSha2 { session_id, cause, .. }
+                                if should_retry(session_id) =>
+                            {
+                                (session_id, cause)
+                            }
+                            EncryptedMessage::MegolmV1AesSha2 { .. }
+                            | EncryptedMessage::OlmV1Curve25519AesSha2 { .. }
+                            | EncryptedMessage::Unknown => return None,
+                        };
 
                     tracing::Span::current().record("session_id", session_id);
 
@@ -1069,11 +1068,9 @@ impl<P: RoomDataProvider> TimelineController<P> {
                                 "Successfully decrypted event that previously failed to decrypt"
                             );
 
-                            let cause = UtdCause::determine(Some(original_json));
-
                             // Notify observers that we managed to eventually decrypt an event.
                             if let Some(hook) = unable_to_decrypt_hook {
-                                hook.on_late_decrypt(&remote_event.event_id, cause).await;
+                                hook.on_late_decrypt(&remote_event.event_id, *utd_cause).await;
                             }
 
                             Some(event)