diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8577e88..1664f81 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -84,6 +84,9 @@ jobs:
           npm install --no-save --no-audit --no-fund playwright@1.63.0
           npx playwright install --with-deps --no-shell chromium
 
+      - name: Web responsive shell smoke test
+        run: npm run smoke:chromium:web-shell
+
       - name: Standard Chromium extension smoke test
         run: npm run smoke:chromium
 
diff --git a/apps/web/src/App.tsx b/apps/web/src/App.tsx
index e4fb087..28824a6 100644
--- a/apps/web/src/App.tsx
+++ b/apps/web/src/App.tsx
@@ -497,14 +497,14 @@ export function App() {
           <span className="brand-mark">D·</span>
           <span>Dockmark</span>
         </button>
-        <nav>
-          <button className={`ghost ${view === "launcher" ? "active" : ""}`} type="button" onClick={() => setView("launcher")}>Launcher</button>
-          <button className={`ghost ${view === "workspaces" ? "active" : ""}`} type="button" onClick={() => setView("workspaces")}>Workspaces</button>
-          <button className={`ghost ${view === "sessions" ? "active" : ""}`} type="button" onClick={() => setView("sessions")}>Sessions</button>
-          <button className={`ghost ${view === "bookmarks" ? "active" : ""}`} type="button" onClick={() => setView("bookmarks")}>Bookmarks</button>
-          <button className={`ghost ${view === "search" ? "active" : ""}`} type="button" onClick={() => setView("search")}>Search</button>
-          <button className={`ghost ${view === "transfer" ? "active" : ""}`} type="button" onClick={() => setView("transfer")}>Transfer</button>
-          <button className={`ghost ${view === "extension" ? "active" : ""}`} type="button" onClick={() => setView("extension")}>Extension</button>
+        <nav className="workspace-section-nav" aria-label="Workspace sections">
+          <button className={`ghost ${view === "launcher" ? "active" : ""}`} type="button" aria-current={view === "launcher" ? "page" : undefined} onClick={() => setView("launcher")}>Launcher</button>
+          <button className={`ghost ${view === "workspaces" ? "active" : ""}`} type="button" aria-current={view === "workspaces" ? "page" : undefined} onClick={() => setView("workspaces")}>Workspaces</button>
+          <button className={`ghost ${view === "sessions" ? "active" : ""}`} type="button" aria-current={view === "sessions" ? "page" : undefined} onClick={() => setView("sessions")}>Sessions</button>
+          <button className={`ghost ${view === "bookmarks" ? "active" : ""}`} type="button" aria-current={view === "bookmarks" ? "page" : undefined} onClick={() => setView("bookmarks")}>Bookmarks</button>
+          <button className={`ghost ${view === "search" ? "active" : ""}`} type="button" aria-current={view === "search" ? "page" : undefined} onClick={() => setView("search")}>Search</button>
+          <button className={`ghost ${view === "transfer" ? "active" : ""}`} type="button" aria-current={view === "transfer" ? "page" : undefined} onClick={() => setView("transfer")}>Transfer</button>
+          <button className={`ghost ${view === "extension" ? "active" : ""}`} type="button" aria-current={view === "extension" ? "page" : undefined} onClick={() => setView("extension")}>Extension</button>
         </nav>
       </header>
 
diff --git a/apps/web/src/main.tsx b/apps/web/src/main.tsx
index 5f0ec4a..031f2ea 100644
--- a/apps/web/src/main.tsx
+++ b/apps/web/src/main.tsx
@@ -14,6 +14,7 @@ import "./bookmark-tags.css";
 import "./inbox.css";
 import "./ui-polish.css";
 import "./light-theme-consistency.css";
+import "./responsive-shell.css";
 
 const root = document.getElementById("root");
 if (!root) throw new Error("Missing #root");
diff --git a/apps/web/src/responsive-shell.css b/apps/web/src/responsive-shell.css
new file mode 100644
index 0000000..6b25bbd
--- /dev/null
+++ b/apps/web/src/responsive-shell.css
@@ -0,0 +1,191 @@
+:root {
+  --dm-private-nav-height: 46px;
+  --dm-secondary-nav-height: 64px;
+  --dm-shell-gutter: 20px;
+}
+
+.shell {
+  width: min(1100px, calc(100% - (2 * var(--dm-shell-gutter))));
+}
+
+.private-utility-bar {
+  height: var(--dm-private-nav-height);
+  min-height: var(--dm-private-nav-height);
+  overflow: hidden;
+  padding-inline: max(var(--dm-shell-gutter), calc((100vw - 1100px) / 2));
+}
+
+.private-utility-brand {
+  flex: 0 0 auto;
+}
+
+.private-utility-bar nav,
+.workspace-section-nav {
+  min-width: 0;
+  overflow-x: auto;
+  overscroll-behavior-inline: contain;
+  scrollbar-width: none;
+  -webkit-overflow-scrolling: touch;
+}
+
+.private-utility-bar nav::-webkit-scrollbar,
+.workspace-section-nav::-webkit-scrollbar {
+  display: none;
+}
+
+.private-utility-bar nav {
+  flex: 0 1 auto;
+  margin-left: auto;
+}
+
+.private-utility-bar nav button,
+.workspace-section-nav .ghost {
+  flex: 0 0 auto;
+  white-space: nowrap;
+}
+
+.topbar {
+  position: sticky;
+  top: var(--dm-private-nav-height);
+  z-index: 25;
+  height: var(--dm-secondary-nav-height);
+  min-height: var(--dm-secondary-nav-height);
+  gap: 18px;
+  background: color-mix(in srgb, var(--dm-bg) 94%, transparent);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
+}
+
+.topbar .brand {
+  flex: 0 0 auto;
+}
+
+.workspace-section-nav {
+  flex: 0 1 auto;
+  max-width: 100%;
+  margin-left: auto;
+  scroll-padding-inline: 8px;
+}
+
+.workspace-section-nav .ghost {
+  scroll-snap-align: start;
+}
+
+.manager-sidebar,
+.search-engine-form {
+  top: calc(var(--dm-private-nav-height) + var(--dm-secondary-nav-height) + 18px);
+}
+
+.command-footer {
+  flex-wrap: wrap;
+}
+
+.command-footer span {
+  flex-wrap: wrap;
+}
+
+.panel-heading {
+  gap: 10px;
+}
+
+@media (max-width: 900px) {
+  :root {
+    --dm-shell-gutter: 16px;
+  }
+
+  .topbar {
+    gap: 10px;
+  }
+
+  .topbar .brand > span:not(.brand-mark) {
+    display: none;
+  }
+
+  .workspace-section-nav {
+    flex: 1 1 auto;
+  }
+
+  .workspace-section-nav .ghost {
+    padding-inline: 10px;
+  }
+}
+
+@media (max-width: 720px) {
+  :root {
+    --dm-shell-gutter: 12px;
+  }
+
+  .private-utility-bar {
+    gap: 10px;
+  }
+
+  .private-utility-bar nav {
+    flex: 1 1 auto;
+  }
+
+  .topbar {
+    gap: 8px;
+  }
+
+  .topbar .brand-mark {
+    width: 30px;
+    height: 30px;
+  }
+
+  .panel-heading {
+    align-items: flex-start;
+    flex-wrap: wrap;
+  }
+
+  .command-footer {
+    gap: 8px;
+  }
+
+  .result {
+    gap: 9px;
+    padding-inline: 8px;
+  }
+
+  .pill {
+    flex: 0 0 auto;
+    white-space: nowrap;
+  }
+}
+
+@media (max-width: 520px) {
+  .topbar .brand {
+    display: none;
+  }
+
+  .workspace-section-nav {
+    flex: 1 1 100%;
+    width: 100%;
+    margin-left: 0;
+  }
+
+  .hero {
+    padding-top: 42px;
+    padding-bottom: 34px;
+  }
+
+  .hero h1 {
+    font-size: clamp(34px, 11vw, 44px);
+  }
+
+  .command {
+    min-height: 56px;
+    padding-left: 13px;
+  }
+
+  .command-shortcuts {
+    display: none;
+  }
+
+  .command-footer > span {
+    width: 100%;
+  }
+
+  .feature-grid {
+    margin-top: 34px;
+  }
+}
diff --git a/package.json b/package.json
index 7270842..ead0115 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,8 @@
     "deploy:dry-run": "npm run prepare:cloudflare-deploy && wrangler deploy --dry-run --outdir .wrangler/dry-run",
     "deploy": "npm run build:web && npm run deploy:built",
     "smoke:chromium": "node scripts/chromium-extension-smoke.mjs",
-    "smoke:chromium:newtab": "node scripts/chromium-newtab-smoke.mjs && node scripts/chromium-newtab-ux-smoke.mjs && node scripts/chromium-newtab-parity-smoke.mjs"
+    "smoke:chromium:newtab": "node scripts/chromium-newtab-smoke.mjs && node scripts/chromium-newtab-ux-smoke.mjs && node scripts/chromium-newtab-parity-smoke.mjs",
+    "smoke:chromium:web-shell": "node scripts/chromium-web-shell-smoke.mjs"
   },
   "devDependencies": {
     "typescript": "^7.0.2",
diff --git a/scripts/chromium-web-shell-smoke.mjs b/scripts/chromium-web-shell-smoke.mjs
new file mode 100644
index 0000000..64dff02
--- /dev/null
+++ b/scripts/chromium-web-shell-smoke.mjs
@@ -0,0 +1,133 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { chromium } from "playwright";
+
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const cssPaths = [
+  "apps/web/src/styles.css",
+  "apps/web/src/theme.css",
+  "apps/web/src/security.css",
+  "apps/web/src/search-engines.css",
+  "apps/web/src/responsive-shell.css",
+];
+const css = (await Promise.all(cssPaths.map((file) => readFile(path.join(root, file), "utf8")))).join("\n");
+
+const utilityButtons = ["Workspace", "Inbox", "Collections", "Duplicates", "Settings", "Sign out"];
+const sectionButtons = ["Launcher", "Workspaces", "Sessions", "Bookmarks", "Search", "Transfer", "Extension"];
+
+function fixture() {
+  return `<!doctype html>
+    <html data-theme="light">
+      <head><meta name="viewport" content="width=device-width, initial-scale=1"><style>${css}</style></head>
+      <body>
+        <div class="private-utility-bar">
+          <a class="private-utility-brand"><span>D·</span><b>Public page</b></a>
+          <nav>${utilityButtons.map((label) => `<button>${label}</button>`).join("")}</nav>
+        </div>
+        <main class="shell">
+          <header class="topbar">
+            <button class="brand brand-button"><span class="brand-mark">D·</span><span>Dockmark</span></button>
+            <nav class="workspace-section-nav">${sectionButtons.map((label) => `<button class="ghost">${label}</button>`).join("")}</nav>
+          </header>
+          <section class="hero">
+            <p class="eyebrow">YOUR PERSONAL LAUNCHER</p>
+            <h1>Everything you return to,<br>one command away.</h1>
+            <div class="command">
+              <span class="search-icon">⌕</span>
+              <input value="github">
+              <span class="command-shortcuts"><kbd>⌘ K</kbd></span>
+            </div>
+          </section>
+          <section class="panel">
+            <div class="panel-heading"><span>Command results</span><span class="muted">Browser bridge · 20 open tabs</span></div>
+            <div class="results">
+              <button class="result result-button"><span class="favicon">↗</span><span class="result-copy"><strong>Example result with a deliberately long title that must stay inside the responsive shell</strong><small>https://example.com/a/very/long/path/that/should/ellipsis</small></span><span class="pill">Open tab</span></button>
+            </div>
+            <div class="command-footer"><span><kbd>↑</kbd><kbd>↓</kbd> select <kbd>Enter</kbd> run <kbd>Tab</kbd> accept bang</span><span><kbd>Shift</kbd>/<kbd>⌘</kbd>/<kbd>Ctrl</kbd>+<kbd>Enter</kbd> new tab <kbd>/</kbd> focus <kbd>Esc</kbd> clear</span></div>
+          </section>
+          <section class="management" style="min-height:1600px">
+            <div class="management-grid">
+              <aside class="manager-sidebar form-card">Sticky sidebar</aside>
+              <div class="manager-main"><div class="form-card" style="height:1400px">Long content</div></div>
+            </div>
+          </section>
+        </main>
+      </body>
+    </html>`;
+}
+
+const browser = await chromium.launch({ channel: "chromium", headless: true });
+try {
+  const page = await browser.newPage();
+
+  for (const width of [1280, 900, 720, 390]) {
+    await page.setViewportSize({ width, height: 720 });
+    await page.setContent(fixture(), { waitUntil: "domcontentloaded" });
+
+    const layout = await page.evaluate(() => {
+      const utility = document.querySelector(".private-utility-bar");
+      const secondary = document.querySelector(".topbar");
+      const sectionNav = document.querySelector(".workspace-section-nav");
+      const utilityNav = document.querySelector(".private-utility-bar nav");
+      const sidebar = document.querySelector(".manager-sidebar");
+      const brand = document.querySelector(".topbar .brand");
+      const brandLabel = document.querySelector(".topbar .brand > span:not(.brand-mark)");
+      if (!(utility instanceof HTMLElement) || !(secondary instanceof HTMLElement) || !(sectionNav instanceof HTMLElement) || !(utilityNav instanceof HTMLElement) || !(sidebar instanceof HTMLElement) || !(brand instanceof HTMLElement) || !(brandLabel instanceof HTMLElement)) {
+        throw new Error("Responsive shell fixture is incomplete.");
+      }
+      return {
+        documentWidth: document.documentElement.scrollWidth,
+        bodyWidth: document.body.scrollWidth,
+        viewportWidth: window.innerWidth,
+        utilityHeight: utility.getBoundingClientRect().height,
+        secondaryHeight: secondary.getBoundingClientRect().height,
+        secondaryTop: getComputedStyle(secondary).top,
+        secondaryPosition: getComputedStyle(secondary).position,
+        sidebarTop: getComputedStyle(sidebar).top,
+        sectionNavOverflowing: sectionNav.scrollWidth > sectionNav.clientWidth,
+        utilityNavOverflowing: utilityNav.scrollWidth > utilityNav.clientWidth,
+        brandDisplay: getComputedStyle(brand).display,
+        brandLabelDisplay: getComputedStyle(brandLabel).display,
+      };
+    });
+
+    assert.ok(layout.documentWidth <= width + 1, `${width}px viewport should not have document-level horizontal overflow.`);
+    assert.ok(layout.bodyWidth <= width + 1, `${width}px viewport should not have body-level horizontal overflow.`);
+    assert.equal(layout.utilityHeight, 46);
+    assert.equal(layout.secondaryHeight, 64);
+    assert.equal(layout.secondaryPosition, "sticky");
+    assert.equal(layout.secondaryTop, "46px");
+    assert.equal(layout.sidebarTop, "128px");
+
+    if (width === 1280) {
+      assert.notEqual(layout.brandLabelDisplay, "none", "Desktop should keep the Dockmark secondary brand label.");
+    }
+    if (width === 720) {
+      assert.equal(layout.brandLabelDisplay, "none", "Tablet layout should reclaim space by hiding the secondary brand label.");
+    }
+    if (width === 390) {
+      assert.equal(layout.brandDisplay, "none", "Phone layout should dedicate the secondary bar to section navigation.");
+      assert.equal(layout.sectionNavOverflowing, true, "Phone section navigation should scroll within its own bar instead of widening the page.");
+      assert.equal(layout.utilityNavOverflowing, true, "Phone utility navigation should scroll within the utility bar instead of widening the page.");
+    }
+
+    await page.evaluate(() => window.scrollTo(0, 900));
+    await page.waitForTimeout(50);
+    const sticky = await page.evaluate(() => {
+      const utility = document.querySelector(".private-utility-bar")?.getBoundingClientRect();
+      const secondary = document.querySelector(".topbar")?.getBoundingClientRect();
+      return { utilityTop: utility?.top, secondaryTop: secondary?.top };
+    });
+    assert.ok(Math.abs((sticky.utilityTop ?? 999) - 0) <= 1, `${width}px utility bar should remain pinned to the viewport top.`);
+    assert.ok(Math.abs((sticky.secondaryTop ?? 999) - 46) <= 1, `${width}px workspace nav should remain pinned directly below the utility bar.`);
+  }
+
+  console.log("✓ Web shell has no document-level horizontal overflow at 1280/900/720/390px");
+  console.log("✓ Utility and workspace navigation remain stacked and sticky while scrolling");
+  console.log("✓ Tablet and phone breakpoints reclaim nav space without clipping the page");
+  console.log("✓ Internal sticky sidebars offset below both navigation bars");
+} finally {
+  await browser.close();
+}