Cursors: Caps Lock gives the drawing tools the crosshair

While Caps Lock is on, the tools whose pointer General > Use Precise
Cursors changes show the crosshair, and the saved preference does not
change. The desktop app reads the lock state on macOS, Windows and
Linux X11 and passes each change to the new view.capsLock command. A
change to view.capsLock or usePreciseCursors through app.run refreshes
the canvas pointer. The view.preciseCursors command is labeled Use
Precise Cursors, so command search finds it by the preference's name.

crates/engine/src/tests/prefs.rs

@@ -389,6 +389,31 @@ fn use_precise_cursors_makes_drawing_cursors_crosshairs() {
     assert_eq!(cursor(&mut s, "eyedropper"), Cursor::Eyedropper);
 }
 
+/// Caps Lock gives the drawing tools the precise crosshair while it is on, and leaves the saved
+/// Use Precise Cursors preference as it was.
+#[test]
+fn caps_lock_gives_drawing_tools_the_crosshair() {
+    use vectorcraft_tools::{Cursor, Mods};
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 400, "height": 400})).unwrap();
+    let cursor = |s: &mut Session, tool: &str| {
+        s.select_tool(tool, ViewInfo::default()).unwrap();
+        s.cursor(vectorcraft_geom::Point::new(300.0, 300.0), Mods::default(), ViewInfo::default())
+    };
+    assert_eq!(s.execute("view.capsLock", &json!({})).unwrap(), json!({"on": false}));
+    assert_eq!(s.execute("view.capsLock", &json!({"on": true})).unwrap(), json!({"on": true}));
+    assert!(!s.prefs.use_precise_cursors, "Caps Lock leaves the preference off");
+    assert_eq!(cursor(&mut s, "pen"), Cursor::Crosshair);
+    assert_eq!(cursor(&mut s, "lasso"), Cursor::Crosshair);
+    assert_eq!(cursor(&mut s, "eyedropper"), Cursor::Crosshair);
+    assert_eq!(cursor(&mut s, "selection"), Cursor::Arrow);
+    assert_eq!(s.execute("view.capsLock", &json!({"on": false})).unwrap(), json!({"on": false}));
+    assert_eq!(cursor(&mut s, "pen"), Cursor::Pen);
+    assert_eq!(cursor(&mut s, "eyedropper"), Cursor::Eyedropper);
+    assert!(s.execute("view.capsLock", &json!({"on": 1})).is_err());
+    assert_eq!(s.execute("view.capsLock", &json!({})).unwrap(), json!({"on": false}));
+}
+
 /// Use Precise Cursors changes the pointer of the tools that have one of their own: off, each shows its own
 /// pointer; on, a crosshair. Every other drawing tool shows a crosshair either way, and the Type tool and the
 /// Scissors over no path keep theirs.