fix(@next/env): include dir in cache key for loadEnvConfig

[sleitor]

Problem

loadEnvConfig in @next/env uses module-level variables to cache the result. The cache guard:

if (combinedEnv && !forceReload) {
  return { combinedEnv, parsedEnv, loadedEnvFiles: cachedLoadedEnvFiles }
}

ignores the dir argument — so when Next.js internally calls loadEnvConfig (with the app directory) before user code runs, then user code calls loadEnvConfig with a different directory (e.g. a monorepo root), the cache returns the previous result for the wrong directory with no warning or error.

This is especially common in monorepo setups where .env files live in a parent directory outside the Next.js app.

Fixes #92040

Fix

Add a cachedDir module-level variable and include it in the cache check:

if (combinedEnv && !forceReload && cachedDir === dir) {
  return { combinedEnv, parsedEnv, loadedEnvFiles: cachedLoadedEnvFiles }
}

cachedDir is updated whenever a fresh load is performed. The existing forceReload: true workaround continues to work.

Testing

Added test/unit/load-env-cache-dir.test.ts covering:

• Distinct directories load their respective .env files
• Different dir without forceReload is no longer silently cached from previous dir
• Same dir without forceReload still correctly uses the cache

[nextjs-bot]

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