===== 1. unit suite with the fix (npx vitest run) =====
 Test Files  76 passed (76)
      Tests  444 passed (444)

===== 2. chromium suite with the fix (CI=1 npx playwright test) =====
[1/6] [chromium] › e2e/browser-compatibility.e2e.ts:61:1 › Should detect nx on the root
[2/6] [chromium] › e2e/browser-compatibility.e2e.ts:77:1 › Should detect the package manager
[3/6] [chromium] › e2e/browser-compatibility.e2e.ts:86:1 › Should detect js workspaces
[4/6] [chromium] › e2e/next-settings.e2e.ts:27:3 › detects Next.js build settings with NETLIFY_NEXT_PLUGIN_SKIP=undefined
[5/6] [chromium] › e2e/next-settings.e2e.ts:27:3 › detects Next.js build settings with NETLIFY_NEXT_PLUGIN_SKIP=
[6/6] [chromium] › e2e/next-settings.e2e.ts:27:3 › detects Next.js build settings with NETLIFY_NEXT_PLUGIN_SKIP=true
  6 passed (2.9s)

===== 3. new unit tests against unpatched file-system.ts and next.ts =====
⎯⎯⎯⎯⎯⎯⎯ Failed Tests 8 ⎯⎯⎯⎯⎯⎯⎯
AssertionError: expected '/repo/repo/app' to be '/repo/app' // Object.is equality
AssertionError: expected '/repo/other/app' to be '/other/app' // Object.is equality
AssertionError: expected '/repo/app/other' to be '/other' // Object.is equality
AssertionError: expected '/repo/ignored/app' to be '/app' // Object.is equality
AssertionError: expected '/repo/app/' to be '/repo/app' // Object.is equality
AssertionError: expected '/repo/repo/app' to be '/repo/app' // Object.is equality
AssertionError: expected [] to deeply equal [ '@netlify/plugin-nextjs' ]
 Test Files  2 failed (2)
      Tests  8 failed | 17 passed (25)

===== 4. new chromium tests against unpatched code =====
  3 failed

===== 5. fix restored: typecheck, lint, format =====
tsc --project tsconfig.build.json: exit 0
Checking formatting...
eslint: exit 0

===== 6. pre-existing failures on unchanged main (tsconfig.test.json) =====
src/build-systems/vite-plus.test.ts(156,16): error TS2722: Cannot invoke an object which is possibly 'undefined'.
src/build-systems/vite-plus.test.ts(170,16): error TS2722: Cannot invoke an object which is possibly 'undefined'.
src/project.test.ts(36,65): error TS2345: Argument of type '"" | SemVer' is not assignable to parameter of type 'object | any[]'.
  Type 'string' is not assignable to type 'object | any[]'.

===== 7. diff against main =====
 packages/build-info/e2e/next-settings.e2e.ts    | 44 +++++++++++++++++++++++++
 packages/build-info/src/browser/file-system.ts  |  7 ++--
 packages/build-info/src/browser/resolve.test.ts | 38 +++++++++++++++++++++
 packages/build-info/src/frameworks/next.test.ts | 10 +++++-
 packages/build-info/src/frameworks/next.ts      |  2 +-
 5 files changed, 97 insertions(+), 4 deletions(-)

===== 8. mutation check on the skip condition =====
With `getEnv('NETLIFY_NEXT_PLUGIN_SKIP') === undefined` in place of the truthiness check,
the whole unit suite still passes (444) while the browser case for an empty value fails:
  [chromium] detects Next.js build settings with NETLIFY_NEXT_PLUGIN_SKIP=  -> 1 failed
That case is why the empty-value variant stays in the browser suite.