Keep a late sidecar off the next photograph

A stored edit that arrived after the view had stepped on was applied to
whatever session was open by then — the next photograph's. The wait now
stops once the open it belongs to is no longer the current one.

ui/dr-ui/src/lib.rs

@@ -805,12 +805,16 @@ pub(crate) fn refresh_export_label(window: &AppWindow) {
 ///
 /// A late arrival redraws, so the image is correct either way; the only
 /// difference is whether it was ever briefly shown at its defaults.
+///
+/// `still_current` is false once the view has moved to another photograph,
+/// whose session this sidecar must not be applied to.
 fn apply_when_ready(
     window: &AppWindow,
     rx: Rc<std::sync::mpsc::Receiver<Option<dr_pipeline::Sidecar>>>,
     session: &Rc<RefCell<Option<DevelopSession>>>,
     rows: &Rc<slint::VecModel<ParamRow>>,
     redraw: &Rc<dyn Fn(&AppWindow)>,
+    still_current: impl Fn() -> bool + 'static,
 ) {
     // Already here — the overwhelmingly common case.
     if let Ok(got) = rx.try_recv() {
@@ -830,6 +834,10 @@ fn apply_when_ready(
         slint::TimerMode::Repeated,
         std::time::Duration::from_millis(50),
         move || {
+            if !still_current() {
+                held.stop();
+                return;
+            }
             let Ok(got) = rx.try_recv() else { return };
             held.stop();
             let Some(w) = weak.upgrade() else { return };
@@ -2858,12 +2866,14 @@ fn wire_remote_open(
                                     // practice it has; `apply_when_ready`
                                     // covers the case where it has not rather
                                     // than blocking the UI thread on a socket.
+                                    let still = current.clone();
                                     apply_when_ready(
                                         &w,
                                         sidecar_rx.clone(),
                                         &session,
                                         &rows,
                                         &redraw,
+                                        move || still.get() == mine,
                                     );
                                     // TRACES: FR-UI-4
                                     // Under the same magnifier as the last