Build: `next.config.ts` with TS import aliases / `baseUrl` fails

This issue was created by an agent analysing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-05-22).

Problem

A next.config.ts that uses TS path aliases / baseUrl in CJS mode fails to build (Custom deploy script failed: undefined). Distinct from #1345 (__dirname redeclaration) — this is about TS path-alias resolution at config-load time.

next.config.ts with import aliases + baseUrl fails to build

Estimated Impact

~1 test failures across the deploy suite.

Affected Test Suites

• test/e2e/app-dir/next-config-ts/import-alias-paths-with-baseurl/next-config-ts-import-alias-paths-with-baseurl-cjs.test.ts

Recommendation

1. Reproduce first in vinext's own test suite. Add a next.config.ts that imports a path alias via tsconfig's paths. Confirm the build fails.

2. Resolve TS aliases when loading next.config.ts. When loading the config in CJS mode, read tsconfig.json paths/baseUrl and pass them to the TS loader so the config file can use aliased imports.

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Part of #1328.