UI.7: keep the newest remembered layout when the list is full

remember() pushed the layout being left and then truncated the list to
64, so with 64 workspaces already remembered it dropped the entry it
had just pushed and the changes were lost. Drop the oldest entries
instead; a test fills the list and checks the last one left survives.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KcHisW1vt6pkVPYbzL6Cpg

crates/ui-egui/src/workspaces.rs

@@ -223,7 +223,9 @@ fn remember(ui: &mut UiState) {
     let w = capture(ui, &current);
     ui.workspace_changes.retain(|x| x.name != current);
     ui.workspace_changes.push(w);
-    ui.workspace_changes.truncate(64);
+    // Over the cap, the oldest go: the layout just kept is the newest.
+    let over = ui.workspace_changes.len().saturating_sub(64);
+    ui.workspace_changes.drain(..over);
 }
 
 /// Switch to workspace `name` as it was left (its changes since it was saved), else as saved.
@@ -603,6 +605,24 @@ mod tests {
         assert!(!ui.control_bar, "Essentials didn't remember the deleted workspace's layout");
     }
 
+    #[test]
+    fn a_full_list_of_remembered_layouts_drops_the_oldest_not_the_newest() {
+        let mut ui = UiState::default();
+        let names: Vec<String> = (0..70).map(|i| format!("W{i}")).collect();
+        for name in &names {
+            save_as(&mut ui, name).unwrap();
+        }
+        for name in &names {
+            switch(&mut ui, name).unwrap();
+            ui.control_bar = true;
+        }
+        switch(&mut ui, ESSENTIALS).unwrap();
+        assert_eq!(ui.workspace_changes.len(), 64);
+        assert!(ui.workspace_changes.iter().all(|w| w.name != "W0"), "the oldest went");
+        switch(&mut ui, "W69").unwrap();
+        assert!(ui.control_bar, "the layout just left is kept");
+    }
+
     #[test]
     fn saving_a_workspace_moves_the_changes_into_it() {
         let mut ui = UiState { control_bar: true, ..Default::default() };