Preserve alternate screen snapshots and speed builds

tests/integration_smoke.rs

@@ -572,6 +572,63 @@ fn live_output_forwards_terminal_control_sequences() {
     );
 }
 
+#[test]
+fn resume_snapshot_preserves_alternate_screen_mode() {
+    let dir = tempfile::tempdir().unwrap();
+    let port = free_udp_port();
+    let config = write_server_config(&dir, port);
+    let mut server = start_server(&dir, &config);
+    let (socket, bootstrap, ok) = direct_attach(&config, port, "read-write");
+
+    let input = Input {
+        bytes: b"printf '\\033[?1049hALT_SNAPSHOT'\n".to_vec(),
+    };
+    send_encrypted(
+        &socket,
+        port,
+        PacketKind::Input,
+        ok.client_id,
+        2,
+        0,
+        &bootstrap.session_key,
+        &protocol::to_body(&input).unwrap(),
+    );
+    let _ = collect_frame_text(&socket, &bootstrap.session_key, 500);
+    let new_socket = UdpSocket::bind("127.0.0.1:0").unwrap();
+    new_socket
+        .set_read_timeout(Some(Duration::from_secs(2)))
+        .unwrap();
+
+    let resume = ResumeRequest {
+        session: "default".to_string(),
+        last_rendered_seq: ok.initial_seq,
+        cols: 80,
+        rows: 24,
+    };
+    send_encrypted(
+        &new_socket,
+        port,
+        PacketKind::ResumeRequest,
+        ok.client_id,
+        3,
+        0,
+        &bootstrap.session_key,
+        &protocol::to_body(&resume).unwrap(),
+    );
+    let (_header, resume_frame) =
+        recv_frame(&new_socket, &bootstrap.session_key).expect("resume response");
+
+    let _ = server.kill();
+    let _ = server.wait();
+
+    assert!(resume_frame.snapshot);
+    assert!(
+        resume_frame.bytes.starts_with(b"\x1b[?1049h"),
+        "snapshot did not enter alternate screen first: {:?}",
+        String::from_utf8_lossy(&resume_frame.bytes)
+    );
+}
+
 #[test]
 fn resume_updates_udp_endpoint_for_roaming() {
     let dir = tempfile::tempdir().unwrap();