perf: skip i18n context setup for build asset requests

[lazerg]

• Resolves initializeI18nContext runs on every request and response times at our ingress go from ~50 ms to 250–500 ms #4144

The nitro request hook sets up the i18n context for every request, including the /_nuxt/* chunks a node-server deployment serves itself. That setup calls useRuntimeConfig(event), which clones the whole runtime config and walks every key looking for env overrides, so a 442-byte JS chunk pays for a full config pass it never reads. The reporter profiled it at ~16.5% of non-idle CPU, with throughput dropping from ~9060 rps on Nuxt 3.15 + i18n 9.5.6 to ~2065 rps on 10.6.0.

The hook now returns early for paths under app.buildAssetsDir, resolved once during plugin setup. Nothing downstream reads the context on that path: nitro serves or 404s build assets before render:before runs, so useI18nContext is never reached for them. The reporter measured ~8290 rps with the same guard, and SSR requests are unaffected.

Summary by CodeRabbit

• Bug Fixes

  • Prevented i18n initialization for build asset requests, improving asset delivery and avoiding unnecessary request processing.
  • Preserved i18n initialization for regular page requests, including applications served from the root path.

• Tests

  • Added coverage for build assets with and without a configured base URL, as well as standard page requests.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9770ceda-0671-4246-b28a-677bc2906144

📥 Commits

Reviewing files that changed from the base of the PR and between d53377d and f863974.

📒 Files selected for processing (5)

• src/runtime/server/plugin.ts
• test/mocks/nuxt.internal-config.ts
• test/server-plugin.test.ts
• test/setup.ts
• vitest.config.test.ts

Included review availability: Your plan provides up to 8 included reviews per hour; 5 remain after this review.

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Walkthrough

The server plugin derives the build-assets path from runtime configuration and skips i18n context initialization for matching requests. New tests cover default and base URLs, page requests, and root asset paths. Test mocks, Vitest aliases, and a global stub support isolated server-plugin testing.

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

Merge Risk: ⚪ Minimal · up to f8639

This localized performance change avoids unnecessary i18n setup for build asset requests without identified functional impact; no actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the primary change: skipping i18n context setup for build asset requests.
Linked Issues check	✅ Passed	The implementation and tests address issue #4144 by skipping i18n setup for build assets while preserving page request handling.
Out of Scope Changes check	✅ Passed	The code, test, mock, and Vitest configuration changes directly support the performance fix described in issue #4144.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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