v3: persist sidebar state via cookie, default closed on tablet/mobile

Sidebar open/close state is now saved to a cookie (neko_sidebar) so it
persists across page reloads. On first visit without a cookie, the
sidebar defaults to closed on tablet and mobile (<=1024px viewport)
and open on desktop. Removes the auto-open-on-resize behavior that
was overriding user preference.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 41 insertions, 1 deletions

diff --git a/frontend-vanilla/src/store.test.ts b/frontend-vanilla/src/store.test.ts
index 33deb7f..799db83 100644
--- a/frontend-vanilla/src/store.test.ts
+++ b/frontend-vanilla/src/store.test.ts
@@ -1,4 +1,4 @@
-import { describe, it, expect, vi } from 'vitest';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { Store } from './store';
 
 describe('Store', () => {
@@ -105,4 +105,44 @@ describe('Store', () => {
         expect(localStorage.getItem('neko-font-theme')).toBe('serif');
         expect(callback).toHaveBeenCalled();
     });
+
+    describe('sidebar cookie persistence', () => {
+        beforeEach(() => {
+            // Clear sidebar cookie
+            document.cookie = 'neko_sidebar=; path=/; max-age=0';
+        });
+
+        it('should persist sidebar state to cookie', () => {
+            const store = new Store();
+            store.setSidebarVisible(false);
+            expect(document.cookie).toContain('neko_sidebar=0');
+
+            store.setSidebarVisible(true);
+            expect(document.cookie).toContain('neko_sidebar=1');
+        });
+
+        it('should read sidebar state from cookie on init', () => {
+            document.cookie = 'neko_sidebar=1; path=/';
+            const store = new Store();
+            expect(store.sidebarVisible).toBe(true);
+
+            document.cookie = 'neko_sidebar=0; path=/';
+            const store2 = new Store();
+            expect(store2.sidebarVisible).toBe(false);
+        });
+
+        it('should default to closed on tablet/mobile when no cookie', () => {
+            // jsdom defaults innerWidth to 0, which is <= 1024
+            const store = new Store();
+            expect(store.sidebarVisible).toBe(false);
+        });
+
+        it('should emit sidebar-toggle when toggling', () => {
+            const store = new Store();
+            const callback = vi.fn();
+            store.on('sidebar-toggle', callback);
+            store.toggleSidebar();
+            expect(callback).toHaveBeenCalled();
+        });
+    });
 });