Swatches panel keeps the art's swatch highlighted after deselecting

Deselecting made the panel jump to the swatch of the paint new art gets
(White). It now keeps the deselected art's swatch until the paints for new
art change (a swatch or colour picked with nothing selected) or another
document shows; selecting other art highlights its swatch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/panels/swatches.rs

@@ -687,7 +687,7 @@ fn body(app: &mut VectorcraftApp, ui: &mut Ui, salt: &'static str) {
     widgets::subheader(ui, tl!("Swatch Tiles"));
     let query = if pstate(ui.ctx(), "swatch-show-find") { widgets::search_field(ui, find_id(), tl!("Find")) } else { String::new() };
     let items = entries(app, kind, &query);
-    let active_swatch = active_swatch(app);
+    let active_swatch = kept_swatch(app, ui, active_swatch(app));
     let focus = focus_swatch(app, ui, active_swatch.as_deref());
     let selected = selection(app, ui);
     // Without a selection the swatch of the active paint is highlighted.
@@ -773,6 +773,29 @@ fn body(app: &mut VectorcraftApp, ui: &mut Ui, salt: &'static str) {
 /// The document and the objects selected in it.
 type SelectedArt = (u64, Vec<u64>);
 
+/// The swatch highlighted for the active paint (`active`): with art selected, its swatch; once the
+/// art is deselected, still that swatch, until another document shows or the paints for new art
+/// change (a swatch or colour picked with nothing selected). Deselecting doesn't jump to the
+/// swatch of the paint new art gets (White).
+fn kept_swatch(app: &VectorcraftApp, ui: &Ui, active: Option<String>) -> Option<String> {
+    let Some(st) = app.session.active() else { return active };
+    let p = &app.session.paint;
+    // The document, and the paints new art gets, which picking with nothing selected changes.
+    let defaults = format!("{}|{:?}|{:?}|{}", st.uid, p.fill, p.stroke, app.session.fill_active);
+    if !st.selection.objects.is_empty() {
+        set_pstate(ui.ctx(), "swatch-kept", Some((defaults, active.clone())));
+        return active;
+    }
+    match pstate::<Option<(String, Option<String>)>>(ui.ctx(), "swatch-kept") {
+        Some((d, kept)) if d == defaults => kept,
+        Some(_) => {
+            set_pstate(ui.ctx(), "swatch-kept", None::<(String, Option<String>)>);
+            active
+        }
+        None => active,
+    }
+}
+
 /// The swatch the tiles scroll to this frame, once: the active paint's swatch when it changed, or
 /// when other art was selected. Selecting other art also clears the panel's own selection, so its
 /// swatch is the one highlighted.
@@ -1905,6 +1928,38 @@ mod tests {
         assert_eq!(focus_swatch(&app, &egui::Ui::new(ctx.clone(), egui::Id::new("t"), egui::UiBuilder::new()), Some("Last Ink")), None);
     }
 
+    /// Deselecting art keeps its swatch highlighted (not the White new art gets) until the paints for
+    /// new art change; selecting other art highlights its swatch.
+    #[test]
+    fn deselecting_keeps_the_arts_swatch_highlighted() {
+        let mut app = app();
+        app.run("swatch.new", json!({"name": "Ink 185", "color": "#e4002b", "spot": true})).unwrap();
+        let id = app.run("shape.rectangle", json!({"x": 0, "y": 0, "width": 50, "height": 50})).unwrap()["id"].clone();
+        app.run("paint.setFill", json!({"ids": [id], "swatch": "Ink 185"})).unwrap();
+        app.run("select.none", json!({})).unwrap();
+        // New art's paints back to the defaults, as for art that came in with a file.
+        app.run("paint.default", json!({})).unwrap();
+        let ctx = context();
+        let ui = egui::Ui::new(ctx.clone(), egui::Id::new("t"), egui::UiBuilder::new());
+        let shown = |app: &VectorcraftApp| kept_swatch(app, &ui, active_swatch(app));
+        assert_ne!(shown(&app).as_deref(), Some("Ink 185"), "nothing selected yet: new art's paint");
+        app.run("select.set", json!({"ids": [id]})).unwrap();
+        assert_eq!(shown(&app).as_deref(), Some("Ink 185"));
+        app.run("select.none", json!({})).unwrap();
+        assert_eq!(shown(&app).as_deref(), Some("Ink 185"), "kept after deselecting");
+        assert_eq!(shown(&app).as_deref(), Some("Ink 185"), "and on later frames");
+        // A colour picked with nothing selected is new art's: its swatch shows.
+        app.run("paint.setFill", json!({"swatch": "Black"})).unwrap();
+        assert_eq!(shown(&app).as_deref(), Some("Black"));
+        // Other art selected (a white one) shows its swatch, and keeps it once deselected.
+        let white = app.run("shape.rectangle", json!({"x": 60, "y": 0, "width": 50, "height": 50})).unwrap()["id"].clone();
+        app.run("paint.setFill", json!({"ids": [white.clone()], "swatch": "White"})).unwrap();
+        app.run("select.set", json!({"ids": [white]})).unwrap();
+        assert_eq!(shown(&app).as_deref(), Some("White"));
+        app.run("select.none", json!({})).unwrap();
+        assert_eq!(shown(&app).as_deref(), Some("White"));
+    }
+
     /// A selected image, or text in a colour no swatch has, highlights no swatch (not None); text in
     /// a swatch's colour highlights that swatch.
     #[test]