feat(stores): add shallow comparison helper for Zustand selectors

Co-Authored-By: Claude Opus 4.6 <[email protected]>

apps/frontend/src/renderer/stores/utils.ts

@@ -0,0 +1,36 @@
+/**
+ * Shallow comparison function for Zustand selectors.
+ * Returns true if a and b are shallowly equal (same reference or same primitives).
+ */
+export function shallow<T>(objA: T, objB: T): boolean {
+  if (Object.is(objA, objB)) {
+    return true;
+  }
+
+  if (
+    typeof objA !== 'object' ||
+    objA === null ||
+    typeof objB !== 'object' ||
+    objB === null
+  ) {
+    return false;
+  }
+
+  const keysA = Object.keys(objA as unknown as object);
+  const keysB = Object.keys(objB as unknown as object);
+
+  if (keysA.length !== keysB.length) {
+    return false;
+  }
+
+  for (const key of keysA) {
+    if (
+      !Object.prototype.hasOwnProperty.call(objB, key) ||
+      !Object.is((objA as any)[key], (objB as any)[key])
+    ) {
+      return false;
+    }
+  }
+
+  return true;
+}