fix: do not generate observability functions with fully prerendered routes

[RihanArfan]

🔗 Linked issue

Followup after #4412 is merged

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Currently the Vercel preset creates a observability function for every route, including ones that are fully prerendered to a static file. The function takes presidence over the prerendered file with the Vercel build output so the prerendered route ends up getting SSR'd anyways.

This PR stops generating the observability route for routes that are prerendered, so they can be served.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
nitro.build	Ready	Preview	Jul 30, 2026 12:04pm

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npm i https://pkg.pr.new/nitro@4497

commit: df902d2

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🧹 Nitpick comments (1)

src/presets/vercel/utils.ts (1)

389-419: 📐 Maintainability & Code Quality | 🔵 Trivial | 🏗️ Heavy lift

Split the new prerender logic into an internal module.

src/presets/vercel/utils.ts now exceeds 570 lines. Move getPrerenderOverrides and the shared path normalization into a focused src/presets/vercel/_prerender.ts module. Import that module directly where needed.

As per coding guidelines, “Split logic across files; avoid long single-file modules (>200 LoC).”

Also applies to: 531-556

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/presets/vercel/utils.ts` around lines 389 - 419, Move
getPrerenderOverrides and its shared path-normalization symbols, including the
relevant slash and index matching constants, from utils.ts into a focused
internal _prerender.ts module. Export only the symbols needed by callers, then
update each usage to import them directly from _prerender.ts while preserving
the existing override behavior.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/presets/vercel/utils.ts`:
- Around line 389-419: Move getPrerenderOverrides and its shared
path-normalization symbols, including the relevant slash and index matching
constants, from utils.ts into a focused internal _prerender.ts module. Export
only the symbols needed by callers, then update each usage to import them
directly from _prerender.ts while preserving the existing override behavior.

---

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 77b77ff and df902d2.

📒 Files selected for processing (5)

• src/presets/vercel/utils.ts
• test/presets/fixtures/slash.ts
• test/presets/vercel.test.ts
• test/unit/vercel-observability-routes.test.ts
• test/unit/vercel-overrides.test.ts