Show a loading bar when checkout is happening (#249)

src/store/appAtoms.ts

@@ -0,0 +1,15 @@
+import { atom } from "jotai";
+
+/**
+ * Atom to store the number of active checkoutVersion mutations.
+ * This is a "primitive" atom that you will update directly.
+ */
+export const activeCheckoutCounterAtom = atom(0);
+
+/**
+ * Derived atom that is true if any checkoutVersion mutation is in progress.
+ * This atom is read-only and derives its state from activeCheckoutCounterAtom.
+ */
+export const isAnyCheckoutVersionInProgressAtom = atom(
+  (get) => get(activeCheckoutCounterAtom) > 0,
+);