diff --git a/app/templates/_header.html b/app/templates/_header.html
index 2fdd79c..6cf325f 100644
--- a/app/templates/_header.html
+++ b/app/templates/_header.html
@@ -37,7 +37,7 @@
   {% if not hide_hamburger %}
   <button class="hamburger-btn"
           :class="{ 'hamburger-desktop-show': sidebarCollapsed }"
-          @click="{{ hamburger_click|default('sidebarCollapsed ? toggleSidebar() : (mobileSidebarOpen = true, sidebarCollapsed = false)') }}"
+          @click="{{ hamburger_click|default('fdHamburgerClick()') }}"
           title="Toggle sidebar">
     <svg width="22" height="22" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
       <line x1="3" y1="6" x2="21" y2="6"/>
diff --git a/app/templates/base.html b/app/templates/base.html
index da33e31..30235c7 100644
--- a/app/templates/base.html
+++ b/app/templates/base.html
@@ -1944,6 +1944,17 @@
         this.sidebarCollapsed = !this.sidebarCollapsed;
       },
 
+      // Hamburger: mobile opens the drawer (assignment expressions are illegal
+      // in the Alpine CSP build, hence this method), desktop toggles collapse.
+      fdHamburgerClick() {
+        if (window.matchMedia('(max-width: 768px)').matches) {
+          this.mobileSidebarOpen = true;
+          this.sidebarCollapsed = false;
+        } else {
+          this.toggleSidebar();
+        }
+      },
+
       closeSidebar() {
         if (this.sidebarPeek) { this.sidebarPeek = false; return; }
         this.sidebarCollapsed = true;
diff --git a/app/templates/settings.html b/app/templates/settings.html
index c8bf7fc..6703830 100644
--- a/app/templates/settings.html
+++ b/app/templates/settings.html
@@ -125,6 +125,21 @@
 .llm-detail .prov-field-row{margin-top:12px;}
 .llm-detail-empty{display:flex;align-items:center;justify-content:center;height:260px;font-size:13px;color:var(--text-dim);text-align:center;padding:0 20px;}
 @media (max-width:760px){.llm-layout{grid-template-columns:1fr;}.llm-list{max-height:220px;}}
+
+/* ── Mobile: full-screen panel + horizontal nav tabs ── */
+@media (max-width:768px){
+  .settings-overlay{background:var(--bg-primary);backdrop-filter:none;}
+  .settings-panel{flex-direction:column;width:100vw;max-width:100vw;height:100dvh;max-height:100dvh;margin:0;border:none;border-radius:0;box-shadow:none;}
+  .settings-nav{width:auto;min-width:0;flex-direction:row;flex-shrink:0;display:flex;align-items:center;overflow-x:auto;border-right:none;border-bottom:1px solid var(--border);padding:6px 8px;gap:4px;overscroll-behavior-x:contain;}
+  .settings-nav-header{display:none;}
+  .settings-nav-item{white-space:nowrap;padding:8px 12px;border-radius:8px;flex-shrink:0;}
+  .settings-content{padding:16px;}
+  .settings-close{top:8px;right:8px;width:44px;height:44px;background:var(--bg-tertiary);}
+  .setting-row{flex-wrap:wrap;}
+  .setting-control{margin-left:0;width:100%;}
+  .prov-grid{grid-template-columns:1fr;}
+  .avatar-section{gap:10px;}
+}
 </style>
 
 <div class="settings-overlay" x-data="settingsInit()" @keydown.escape="historyBack()">
diff --git a/e2e/mobile_regression.spec.js b/e2e/mobile_regression.spec.js
new file mode 100644
index 0000000..c4dd20d
--- /dev/null
+++ b/e2e/mobile_regression.spec.js
@@ -0,0 +1,74 @@
+// Mobile regression: hamburger opens the sidebar drawer, settings page fits viewport.
+const { test, expect } = require('@playwright/test');
+const FD_BASE = process.env.FD_BASE_URL || 'http://localhost:8080';
+const USER = process.env.FD_USER || 'e2e@flowdeck.test';
+const PASS = process.env.FD_PASS || 'e2e-pass-123';
+
+async function login(page) {
+  await page.goto(`${FD_BASE}/auth/login?provider=local`, { waitUntil: 'domcontentloaded' });
+  await page.fill('#email', USER);
+  await page.fill('#password', PASS);
+  await page.click('.btn-primary');
+  const ok = await page.waitForURL('**/workspaces', { timeout: 10000 }).then(() => true).catch(() => false);
+  if (!ok) {
+    const resp = await page.request.post(`${FD_BASE}/auth/register`, { data: { email: USER, password: PASS, name: 'E2E Mobile' } });
+    if (!resp.ok() && resp.status() !== 409) throw new Error(`register ${resp.status()}`);
+    await page.goto(`${FD_BASE}/auth/login?provider=local`, { waitUntil: 'domcontentloaded' });
+    await page.fill('#email', USER);
+    await page.fill('#password', PASS);
+    await page.click('.btn-primary');
+    await page.waitForURL('**/workspaces', { timeout: 10000 });
+  }
+}
+
+test.describe('mobile', () => {
+  test.use({ viewport: { width: 390, height: 844 } });
+
+  test('hamburger opens mobile sidebar drawer', async ({ page }) => {
+    const errs = [];
+    page.on('pageerror', (e) => errs.push(e.message));
+    await login(page);
+    await page.goto(`${FD_BASE}/library`, { waitUntil: 'domcontentloaded' });
+
+    const burger = page.locator('.hamburger-btn');
+    await expect(burger).toBeVisible();
+
+    // Sidebar starts off-canvas
+    const sidebar = page.locator('#sidebar');
+    const boxBefore = await sidebar.boundingBox();
+    expect(boxBefore.x).toBeLessThan(0);
+
+    await burger.click();
+    await expect(sidebar).toHaveClass(/mobile-open/, { timeout: 5000 });
+    const boxAfter = await sidebar.boundingBox();
+    expect(boxAfter.x).toBeGreaterThanOrEqual(0);
+    expect(errs).toEqual([]);
+
+    // Overlay tap closes it
+    await page.locator('.sidebar-overlay').click({ position: { x: 350, y: 400 } });
+    await expect(sidebar).not.toHaveClass(/mobile-open/, { timeout: 5000 });
+  });
+
+  test('settings page fits mobile viewport', async ({ page }) => {
+    await login(page);
+    await page.goto(`${FD_BASE}/settings`, { waitUntil: 'domcontentloaded' });
+    const panel = page.locator('.settings-panel');
+    await expect(panel).toBeVisible();
+
+    const box = await panel.boundingBox();
+    expect(box.width).toBeLessThanOrEqual(390);
+    expect(box.height).toBeLessThanOrEqual(844);
+
+    // Nav becomes horizontal tabs: nav wider than tall
+    const navBox = await page.locator('.settings-nav').boundingBox();
+    expect(navBox.width).toBeGreaterThan(navBox.height);
+
+    // Tapping a nav item still switches sections
+    await page.locator('.settings-nav-item', { hasText: 'Tags' }).click();
+    await expect(page.locator('h2', { hasText: 'Tags' }).first()).toBeVisible();
+
+    // No horizontal page overflow
+    const overflow = await page.evaluate(() => document.documentElement.scrollWidth - document.documentElement.clientWidth);
+    expect(overflow).toBeLessThanOrEqual(0);
+  });
+});