diff --git a/web/src/lib/stores/mobileNav.svelte.ts b/web/src/lib/stores/mobileNav.svelte.ts
new file mode 100644
index 00000000..641750bc
--- /dev/null
+++ b/web/src/lib/stores/mobileNav.svelte.ts
@@ -0,0 +1,22 @@
+// Open/close state for the off-canvas mobile navigation drawer.
+// Mounted once from Shell.svelte; toggled by the hamburger button.
+
+let _open = $state(false);
+
+export const mobileNav = {
+  get value(): boolean {
+    return _open;
+  }
+};
+
+export function openMobileNav(): void {
+  _open = true;
+}
+
+export function closeMobileNav(): void {
+  _open = false;
+}
+
+export function toggleMobileNav(): void {
+  _open = !_open;
+}