diff --git a/components/InteractiveViewer.massive-scaling.test.tsx b/components/InteractiveViewer.massive-scaling.test.tsx
new file mode 100644
index 000000000..bc08e7115
--- /dev/null
+++ b/components/InteractiveViewer.massive-scaling.test.tsx
@@ -0,0 +1,137 @@
+import React from 'react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { render, fireEvent, screen } from '@testing-library/react';
+import InteractiveViewer from './InteractiveViewer';
+
+// Mock portal tooltip dependencies
+vi.mock('./dashboard/VisualizationTooltip', () => ({
+  default: ({ children }: { children: React.ReactNode }) => (
+    <div data-testid="visualization-tooltip">{children}</div>
+  ),
+}));
+
+vi.mock('framer-motion', () => ({
+  AnimatePresence: ({ children }: { children: React.ReactNode }) => <>{children}</>,
+}));
+
+function generateMassiveDataset(count: number) {
+  return Array.from({ length: count }, (_, i) => (
+    <div
+      key={i}
+      className="interactive-tower"
+      data-date={`2025-01-${String((i % 28) + 1).padStart(2, '0')}`}
+      data-count={String(i)}
+      data-metric={i % 2 === 0 ? 'Peak day' : 'Active day'}
+    >
+      Tower {i}
+    </div>
+  ));
+}
+
+describe('InteractiveViewer Massive Scaling', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('renders thousands of interactive towers without crashing', () => {
+    render(
+      <InteractiveViewer>
+        <div>{generateMassiveDataset(5000)}</div>
+      </InteractiveViewer>
+    );
+
+    expect(screen.getByText('Tower 0')).toBeInTheDocument();
+    expect(screen.getByText('Tower 4999')).toBeInTheDocument();
+  });
+
+  it('renders all parallax particles under heavy content load', () => {
+    const { container } = render(
+      <InteractiveViewer>
+        <div>{generateMassiveDataset(3000)}</div>
+      </InteractiveViewer>
+    );
+
+    const backgroundLayer = container.querySelector('[data-testid="parallax-bg-layer"]');
+
+    expect(backgroundLayer).toBeTruthy();
+
+    // 20 deterministic particles + cursor glow
+    const particleDivs = backgroundLayer?.querySelectorAll('div') ?? [];
+
+    expect(particleDivs.length).toBeGreaterThanOrEqual(21);
+  });
+
+  it('supports repeated zoom operations at extreme bounds', () => {
+    const { container } = render(
+      <InteractiveViewer>
+        <div>Heavy Content</div>
+      </InteractiveViewer>
+    );
+
+    const viewer = container.firstChild as HTMLElement;
+
+    for (let i = 0; i < 100; i++) {
+      fireEvent.keyDown(viewer, { key: '+' });
+    }
+
+    const contentLayer = container.querySelector('[style*="scale"]') as HTMLElement;
+
+    expect(contentLayer.style.transform).toContain('scale(3)');
+
+    for (let i = 0; i < 200; i++) {
+      fireEvent.keyDown(viewer, { key: '-' });
+    }
+
+    expect(contentLayer.style.transform).toContain('scale(0.5)');
+  });
+
+  it('handles extreme keyboard panning without layout failure', () => {
+    const { container } = render(
+      <InteractiveViewer>
+        <div>{generateMassiveDataset(1000)}</div>
+      </InteractiveViewer>
+    );
+
+    const viewer = container.firstChild as HTMLElement;
+
+    for (let i = 0; i < 500; i++) {
+      fireEvent.keyDown(viewer, { key: 'ArrowRight' });
+      fireEvent.keyDown(viewer, { key: 'ArrowDown' });
+    }
+
+    const contentLayer = container.querySelector('[style*="translate"]') as HTMLElement;
+
+    expect(contentLayer.style.transform).toContain('translate');
+  });
+
+  it('shows tooltip correctly for items within massive datasets', async () => {
+    const { container } = render(
+      <InteractiveViewer>
+        <div>{generateMassiveDataset(2500)}</div>
+      </InteractiveViewer>
+    );
+
+    const tower = container.querySelector('.interactive-tower') as HTMLElement;
+
+    expect(tower).toBeTruthy();
+
+    tower.getBoundingClientRect = vi.fn(() => ({
+      left: 100,
+      top: 100,
+      width: 20,
+      height: 40,
+      right: 120,
+      bottom: 140,
+      x: 100,
+      y: 100,
+      toJSON: () => {},
+    }));
+
+    fireEvent.pointerMove(tower, {
+      clientX: 110,
+      clientY: 110,
+    });
+
+    expect(await screen.findByTestId('visualization-tooltip')).toBeInTheDocument();
+  });
+});