diff --git a/src/lib/components/Sidebar.svelte b/src/lib/components/Sidebar.svelte
index ede14d9..87a5137 100644
--- a/src/lib/components/Sidebar.svelte
+++ b/src/lib/components/Sidebar.svelte
@@ -700,7 +700,7 @@
 
 <svelte:window onclick={handleWindowClick} onkeydown={(e) => { if (e.key === 'Escape') iconPickerNotebook = null; }} />
 
-<aside class="sidebar" class:collapsed={$sidebarCollapsed} class:mobile={isMobile} class:nav-empty={!anyNavItem}>
+<aside class="sidebar" class:collapsed={!isMobile && $sidebarCollapsed} class:mobile={isMobile} class:nav-empty={!anyNavItem}>
 	{#if !isMobile}
 	<div class="sidebar-header">
 		<button class="collapse-btn" onclick={() => ($sidebarCollapsed = !$sidebarCollapsed)} title="Toggle sidebar">
@@ -721,7 +721,7 @@
 	</div>
 	{/if}
 
-	{#if !$sidebarCollapsed}
+	{#if isMobile || !$sidebarCollapsed}
 		{#if anyNavItem}
 		<nav class="sidebar-nav">
 			{#if $appConfig?.show_all_notes !== false}
diff --git a/tests/mobile-sidebar.test.mjs b/tests/mobile-sidebar.test.mjs
new file mode 100644
index 0000000..599b2c9
--- /dev/null
+++ b/tests/mobile-sidebar.test.mjs
@@ -0,0 +1,115 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import test from 'node:test';
+import { createContext, Script } from 'node:vm';
+import { compile, parse } from 'svelte/compiler';
+import { get, writable } from 'svelte/store';
+
+const source = await readFile(
+  new URL('../src/lib/components/Sidebar.svelte', import.meta.url),
+  'utf8'
+);
+const ast = parse(source, { modern: true });
+
+function elementWithClass(nodes, className) {
+  return nodes.find((node) => node.attributes?.some((attribute) =>
+    attribute.name === 'class' && attribute.value[0]?.data === className
+  ));
+}
+
+const aside = elementWithClass(ast.fragment.nodes, 'sidebar');
+const blocks = aside.fragment.nodes.filter((node) => node.type === 'IfBlock');
+const content = blocks.find((node) => elementWithClass(node.consequent.nodes, 'section'));
+const header = blocks.find((node) => elementWithClass(node.consequent.nodes, 'sidebar-header'));
+const toggle = elementWithClass(
+  elementWithClass(header.consequent.nodes, 'sidebar-header').fragment.nodes,
+  'collapse-btn'
+);
+
+function expressionScript(expression) {
+  assert.ok(expression, 'expected a component expression');
+  return new Script(`(${source.slice(expression.start, expression.end)})`);
+}
+
+// Execute the actual template conditions, not a copy of the collapse logic.
+const expressions = {
+  contentVisible: expressionScript(content.test),
+  collapsedClass: expressionScript(aside.attributes.find((attribute) =>
+    attribute.type === 'ClassDirective' && attribute.name === 'collapsed'
+  ).expression),
+  toggleVisible: expressionScript(header.test)
+};
+const toggleScript = expressionScript(
+  toggle.attributes.find((attribute) => attribute.name === 'onclick').value.expression
+);
+
+function sidebarContext(isMobile, stored) {
+  const sidebarCollapsed = writable(stored);
+  const context = createContext({
+    isMobile,
+    get $sidebarCollapsed() { return get(sidebarCollapsed); },
+    set $sidebarCollapsed(value) { sidebarCollapsed.set(value); }
+  });
+  return { context, sidebarCollapsed };
+}
+
+function evaluate(context) {
+  return Object.fromEntries(Object.entries(expressions).map(([name, script]) =>
+    [name, script.runInContext(context)]
+  ));
+}
+
+const scenarios = [
+  {
+    platform: 'desktop', isMobile: false,
+    expanded: { contentVisible: true, collapsedClass: false, toggleVisible: true },
+    collapsed: { contentVisible: false, collapsedClass: true, toggleVisible: true }
+  },
+  {
+    platform: 'mobile', isMobile: true,
+    expanded: { contentVisible: true, collapsedClass: false, toggleVisible: false },
+    collapsed: { contentVisible: true, collapsedClass: false, toggleVisible: false }
+  }
+];
+
+for (const scenario of scenarios) {
+  for (const stored of [false, true]) {
+    test(`${scenario.platform} navigation with stored sidebar_collapsed=${stored}`, () => {
+      const { context, sidebarCollapsed } = sidebarContext(scenario.isMobile, stored);
+
+      assert.deepEqual(evaluate(context), stored ? scenario.collapsed : scenario.expanded);
+      assert.equal(get(sidebarCollapsed), stored, 'rendering must preserve the stored preference');
+    });
+  }
+
+  test(`${scenario.platform} navigation follows late false -> true -> false store updates`, () => {
+    const { context, sidebarCollapsed } = sidebarContext(scenario.isMobile, false);
+
+    assert.deepEqual(evaluate(context), scenario.expanded);
+    sidebarCollapsed.set(true);
+    assert.deepEqual(evaluate(context), scenario.collapsed);
+    assert.equal(get(sidebarCollapsed), true, 'rendering must not reset the loaded preference');
+    sidebarCollapsed.set(false);
+    assert.deepEqual(evaluate(context), scenario.expanded);
+    assert.equal(get(sidebarCollapsed), false);
+  });
+}
+
+test('desktop collapse toggle still collapses and expands the sidebar', () => {
+  const { context, sidebarCollapsed } = sidebarContext(false, false);
+  const toggleSidebar = toggleScript.runInContext(context);
+
+  toggleSidebar();
+  assert.equal(get(sidebarCollapsed), true);
+  assert.deepEqual(evaluate(context), scenarios[0].collapsed);
+  toggleSidebar();
+  assert.equal(get(sidebarCollapsed), false);
+  assert.deepEqual(evaluate(context), scenarios[0].expanded);
+});
+
+test('Sidebar compiles for the client', () => {
+  assert.doesNotThrow(() => compile(source, {
+    filename: 'src/lib/components/Sidebar.svelte',
+    generate: 'client'
+  }));
+});