root is overridden with a stale directory when one process resolves a second app's Vite config #17197

Describe the bug

packages/kit/src/exports/vite/index.js captures the working directory once,
when the module is first evaluated:

// packages/kit/src/exports/vite/index.js:58 (main and 2.70.3)
const cwd = posixify(process.cwd());

and the config hook returns it as the project root:

// :333
root: cwd,

A tool that resolves more than one app's Vite config in the same process
therefore gets the first app's directory as the root of every later app. When
@sveltejs/load-config (the loader svelte-check uses) resolves a config, it
changes into that app's directory and passes root explicitly:

// @sveltejs/load-config@0.2.3 dist/src/index.js:125-127
const changeBack = changeCwd(root);
try {
    const resolved = await vite.resolveConfig({ root, configFile: configFilePath, logLevel: 'error' }, 'serve');

Kit's module is already cached from the first app, so its cwd still names that
app. The hook returns root: cwd, warn_overridden_config (:502) finds the
explicit root replaced, and prints:

The following Vite config options will be overridden by SvelteKit:
  - root

The warning is accurate: Vite computes the resolved root from config.root
after the config hooks run, so the second app's resolved config really is rooted
in the first app's directory. The same module-level cwd feeds server.fs.allow
through searchForWorkspaceRoot(cwd) and the paths process_config resolves
when options are passed through the Vite config. (svelte-check itself still
gets the right options, because it reads api.options, which kit loads from
svelte.config.js in the directory load-config changed into.)

It needs the apps to share one @sveltejs/kit install, as in a workspace, so
that a single module instance serves every config. A single app, or apps with
separate installs, never shows it, which is likely why #16293 could not be
reproduced in a fresh app.

The other reports of this message, #13376 and #15987, were the Windows
path-separator false positive fixed by #16037 in 2.65.2. This one reproduces on
macOS on 2.70.3, with that fix present.

Reproduction

https://github.com/rymskip/sveltekit-root-override-repro

Two SvelteKit apps in an npm workspace sharing one kit install. load-both.mjs
resolves each app's config in turn with @sveltejs/load-config.

npm install
npm run repro

Resolving a prints nothing; resolving b prints the warning above. Neither app
sets root.

Logs

> repro
> cd apps/a && node ../../load-both.mjs

resolving a
resolving b
The following Vite config options will be overridden by SvelteKit:
  - root

System Info

  System:
    OS: macOS 26.7
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
    Memory: 14.38 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 26.6.0
    npm: 11.18.0
  npmPackages:
    @sveltejs/kit: 2.70.3 => 2.70.3
    @sveltejs/load-config: 0.2.3 => 0.2.3
    @sveltejs/vite-plugin-svelte: 7.3.1 => 7.3.1
    svelte: 5.57.1 => 5.57.1
    vite: 8.3.0 => 8.3.0

Severity

annoyance

Additional Information

• Where we hit it: svelte-check in one app of a monorepo whose apps alias each
  other's src/lib through kit.alias. It prints the warning once per sibling
  app config its ConfigLoader.loadConfig reaches, and the check itself passes.
• A possible fix: derive the root inside the config hook from the config being
  resolved (config.root, falling back to process.cwd() at that moment) rather
  than from the module-level constant. load-config notes that changing directory
  "is only necessary for SvelteKit < 3", so the constant may already be on its
  way out.
• load-config passes logLevel: 'error', but the warning goes straight to
  console.error, so the level cannot quiet it.