Client-side navigation shows 404 on Vercel deployment, but page reload works correctly

[Arifulislam5577]

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Issue Body

Environment

• Docus version: [latest]
• Nuxt version: ^4.3.1
• Deployment target: Vercel
• Node.js version: v24.14.1
• Package manager: bun - v1.3.14

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Describe the bug

I built a documentation project using Docus and deployed it on Vercel. The deployment succeeds and the initial page loads correctly. However, there is a routing issue:

• ✅ Direct page load (full reload / entering URL in address bar): The page renders correctly with all content.
• ❌ Client-side navigation (clicking sidebar/internal links): Shows a 404 page instead of the target content.
• ✅ After reloading the 404 page (F5 / hard refresh): The correct page content appears.

In short, the content exists and is served correctly on server-side/full page load, but client-side route transitions (SPA-style navigation) fail with a 404 error.

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Steps to reproduce

1. Clone the project: https://github.com/StaticMania/optim-ai-docs
2. Deploy the project to Vercel (zero-config or standard Nuxt/Vercel setup)
3. Visit the live site: https://optimai-docs.vercel.app/
4. Click any sidebar/navigation link to navigate to another page
5. Observe: 404 page is shown
6. Reload the page (F5)
7. Observe: Correct page content is now displayed

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Expected behavior

Client-side navigation (clicking internal links in the sidebar or content) should render the target page without requiring a full page reload, just like it works in local development mode.

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Actual behavior

• Clicking any internal link / sidebar navigation triggers a 404 error page.
• Reloading the page (hard refresh) shows the correct content.
• This only happens on the Vercel deployment — local development (npm run dev) works perfectly.

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Live Demo

🔗 Production URL: https://optimai-docs.vercel.app/

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Additional context

• This issue only occurs in the production deployment on Vercel.
• Local development (dev mode) does not have this problem — all navigation works as expected.
• The issue seems to be related to how client-side routing / payload fetching interacts with the Vercel deployment.

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