Vitest integration CI shards by test file, so the 340-test App Router integration file becomes one oversized scheduling unit. That makes the slowest shard depend on one monolithic file even after adding native shards.
Split the App Router integration coverage into focused files and increase the integration matrix to four native Vitest shards. This keeps fileParallelism disabled for shared-fixture safety while giving CI smaller scheduling units to distribute.
Validation: vp check tests/app-router-*.test.ts vite.config.ts .github/workflows/ci.yml; vp test run --project integration tests/app-router-client-preloading.test.ts tests/app-router-dev-server.test.ts tests/app-router-external-rewrite.test.ts tests/app-router-font-google-prod.test.ts tests/app-router-isr-codegen.test.ts tests/app-router-malformed-url.test.ts tests/app-router-metadata-routes.test.ts tests/app-router-middleware-next-request.test.ts tests/app-router-next-config-codegen.test.ts tests/app-router-next-config-dev.test.ts tests/app-router-origin-check.test.ts tests/app-router-production-build.test.ts tests/app-router-production-server.test.ts tests/app-router-rsc-flight-hint.test.ts tests/app-router-rsc-plugin.test.ts tests/app-router-static-export.test.ts tests/app-router-worker-entry.test.ts
Nathan Nguyen