Preserve restored screen during ticket reattach

src/bin/dosh-server.rs

@@ -813,6 +813,10 @@ fn attach_snapshot(session: &Session, cols: u16, rows: u16) -> Vec<u8> {
     screen_snapshot(session.parser.screen())
 }
 
+fn restored_screen_is_pending_reattach(session: &Session) -> bool {
+    session.restored_screen.is_some()
+}
+
 fn mode_allows_terminal_updates(mode: &str) -> bool {
     mode != "view-only" && mode != "forward-only"
 }
@@ -3707,7 +3711,7 @@ async fn broadcast_output(
         // short wall-clock age so low-throughput prompt/TUI changes persist
         // quickly while large bursts still avoid per-packet disk writes. The
         // actual file write happens after the lock is dropped.
-        if session.persistent {
+        if session.persistent && !restored_screen_is_pending_reattach(session) {
             session.bytes_since_persist = session
                 .bytes_since_persist
                 .saturating_add(output.bytes.len());
@@ -4060,7 +4064,10 @@ fn flush_persistent_screens(state: &Arc<Mutex<ServerState>>) {
         let sessions_dir = locked.sessions_dir();
         let mut to_write: Vec<(String, u16, u16, u64, Vec<u8>)> = Vec::new();
         for (name, session) in locked.sessions.iter_mut() {
-            if !session.persistent || session.output_seq == session.last_persisted_seq {
+            if !session.persistent
+                || restored_screen_is_pending_reattach(session)
+                || session.output_seq == session.last_persisted_seq
+            {
                 continue;
             }
             session.bytes_since_persist = 0;
@@ -4411,6 +4418,20 @@ mod tests {
         let session = locked.sessions.get("work").unwrap();
         assert!(session.restored_screen.is_some());
         assert_eq!(attach_snapshot(session, 80, 24), restored);
+        assert_eq!(
+            session.last_persisted_seq, 7,
+            "pre-reattach PTY output must not overwrite the persisted restored screen"
+        );
+        drop(locked);
+
+        flush_persistent_screens(&state);
+
+        let locked = state.lock().unwrap();
+        let session = locked.sessions.get("work").unwrap();
+        assert_eq!(
+            session.last_persisted_seq, 7,
+            "periodic flush must not replace restored screen before client-visible output"
+        );
     }
 
     #[test]