fix(vercel): prevent caching missing public assets

[ryoid]

🔗 Linked issue

Fixes #4427

❓ 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

This adds a no-store 404 after the filesystem check so missing assets don't fall through with immutable caching.

This follows the same approach as SvelteKit.

📝 Checklist

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

[vercel]

@ryoid is attempting to deploy a commit to the Nitro Team on Vercel.

A member of the Team first needs to authorize it.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 813e416c-c505-46f1-9e6b-2bfbe6a064cf

📥 Commits

Reviewing files that changed from the base of the PR and between 77b77ff and 28b93f4.

📒 Files selected for processing (2)

• src/presets/vercel/utils.ts
• test/presets/vercel.test.ts

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📝 Walkthrough

Walkthrough

The Vercel preset now generates escaped public-asset route patterns, caches existing immutable assets, and returns uncached 404 responses for missing assets after filesystem handling. Tests update the route snapshot and verify the generated 404 rule.

Changes

Vercel public asset routing

Layer / File(s)	Summary
Build public asset route sources src/presets/vercel/utils.ts	generateBuildConfig filters non-fallthrough public assets and builds regex-safe route sources.
Cache and missing-asset routing src/presets/vercel/utils.ts, test/presets/vercel.test.ts	Vercel routes cache matching assets before filesystem handling and emit uncached 404 responses for missing assets; snapshots and assertions cover the generated configuration.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• nitrojs/nitro#4432: Adds immutable static file generation under the Vercel immutable namespace, related to this PR’s public asset routing.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses conventional commit format and accurately describes the Vercel caching fix.
Description check	✅ Passed	The description clearly matches the PR's bug fix and explains the no-store 404 behavior.
Linked Issues check	✅ Passed	The code changes implement the linked issue's requirement to stop immutable caching from reaching HTML fallbacks and return an uncached 404.
Out of Scope Changes check	✅ Passed	The changes stay focused on Vercel public-asset routing and tests, with no unrelated additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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