diff --git a/packages/web/src/pages/Signin.tsx b/packages/web/src/pages/Signin.tsx
index 2f48ccff..2f19147a 100644
--- a/packages/web/src/pages/Signin.tsx
+++ b/packages/web/src/pages/Signin.tsx
@@ -430,10 +430,14 @@ export function Signin({ initialMagicLink = false }: { initialMagicLink?: boolea
     <div className="min-h-screen bg-gradient-to-br from-gray-900 via-gray-800 to-gray-900 flex items-center justify-center p-4 relative overflow-hidden">
       {/* Static gradient background - optimized for all browsers */}
       <div className="lagoon-caustics"></div>
-      <div className="max-w-md w-full relative z-10">
+      {/* Design religion: fit the window. On large screens the branding sits
+          BESIDE the form (wider, 2-column) so the page never needs vertical
+          scrolling; on small screens it stacks above as before. */}
+      <div className="w-full max-w-md lg:max-w-4xl relative z-10">
+       <div className="lg:grid lg:grid-cols-2 lg:gap-12 lg:items-center">
         {/* Header */}
-        <div className="text-center mb-8 animate-in fade-in slide-in-from-top-4 duration-500">
-          <Link to="/" className="inline-flex items-center justify-center mb-6 hover:opacity-90 transition-all duration-300 hover:scale-105 group">
+        <div className="text-center lg:text-left mb-8 lg:mb-0 animate-in fade-in slide-in-from-top-4 duration-500">
+          <Link to="/" className="inline-flex items-center justify-center lg:justify-start mb-6 hover:opacity-90 transition-all duration-300 hover:scale-105 group">
             <img src="/favicon.svg" alt="GraphDone Logo" className="h-12 w-12 sm:h-16 sm:w-16 drop-shadow-lg group-hover:drop-shadow-2xl transition-all duration-300" />
             <span className="ml-3 sm:ml-4 text-4xl sm:text-5xl font-bold bg-gradient-to-r from-teal-400 via-cyan-400 to-blue-500 bg-clip-text text-transparent drop-shadow-2xl tracking-tight">GraphDone</span>
           </Link>
@@ -961,6 +965,7 @@ export function Signin({ initialMagicLink = false }: { initialMagicLink?: boolea
             </div>
           )}
         </form>
+       </div>
 
         {/* Development Mode - Default Credentials */}
         {showDefaultCredentials && (
diff --git a/tests/e2e/signup-fit.spec.ts b/tests/e2e/signup-fit.spec.ts
new file mode 100644
index 00000000..2f7799d3
--- /dev/null
+++ b/tests/e2e/signup-fit.spec.ts
@@ -0,0 +1,45 @@
+import { test, expect } from '@playwright/test';
+import { getBaseURL } from '../helpers/auth';
+
+/**
+ * Responsive "fit the window" religion (@signup-fit): on a large screen the
+ * /signup (magic-link) branding sits BESIDE the form (wider, 2-column) so the
+ * auth flow fits without vertical scrolling; on a phone it stacks with no
+ * horizontal overflow.
+ *
+ * The absolute "documentElement has no vertical scroll" assertion lives in the
+ * live cloud audit (production has no dev-only chrome — the HTTP "insecure
+ * connection" banner and the "Default Accounts" box only render in dev and
+ * would inflate a dev-server measurement). Here we verify the structural fix:
+ * the 2-column layout is active and the form itself fits the viewport height.
+ */
+test.describe('auth page fits the window @signup-fit', () => {
+  test('large screen: branding sits beside the form (2-column) @1600x1000', async ({ page }) => {
+    await page.setViewportSize({ width: 1600, height: 1000 });
+    await page.goto(`${getBaseURL()}/signup`, { waitUntil: 'networkidle' });
+    const form = page.locator('form').first();
+    const header = page.getByRole('heading', { name: /welcome back/i }).first();
+    await form.waitFor({ timeout: 10_000 });
+    const fb = await form.boundingBox();
+    const hb = await header.boundingBox();
+    if (!fb || !hb) throw new Error('missing form/header');
+    // Side-by-side: the heading sits to the LEFT of the form (separate columns),
+    // and they share the same row (vertical overlap) rather than stacking.
+    expect(hb.x + hb.width, `header right (${Math.round(hb.x + hb.width)}) left of form (${Math.round(fb.x)})`).toBeLessThanOrEqual(fb.x + 8);
+    const verticalOverlap = Math.min(hb.y + hb.height, fb.y + fb.height) - Math.max(hb.y, fb.y);
+    expect(verticalOverlap, 'header and form share the row').toBeGreaterThan(0);
+    // The form alone fits comfortably within a 1000px-tall window.
+    expect(fb.height, `form height ${Math.round(fb.height)} fits the window`).toBeLessThanOrEqual(940);
+  });
+
+  test('phone: stacks with no horizontal overflow @360x740', async ({ page }) => {
+    await page.setViewportSize({ width: 360, height: 740 });
+    await page.goto(`${getBaseURL()}/signup`, { waitUntil: 'networkidle' });
+    await page.waitForSelector('form', { timeout: 10_000 });
+    const m = await page.evaluate(() => ({
+      scrollW: document.documentElement.scrollWidth,
+      clientW: document.documentElement.clientWidth,
+    }));
+    expect(m.scrollW, `scrollW ${m.scrollW} should not exceed clientW ${m.clientW}`).toBeLessThanOrEqual(m.clientW + 1);
+  });
+});