fix: JS/TS config execution uses npx inside pnpm, causing failures due to npm warnings on stderr

[krema]

Syncpack version

14.0.0-alpha.32

Operating system(s)

Mac

Steps to reproduce

1. Use pnpm as the package manager.
2. Add a JS/TS-based syncpack config (for example .syncpackrc.js or .syncpackrc.cjs):

module.exports = {
  semverGroups: [
    { dependencyTypes: ["peer"], range: "^" }
  ]
};

3. Run syncpack via pnpm:

pnpm exec syncpack fix --config .syncpackrc.cjs

Expected behavior

• syncpack should successfully load and execute the JS/TS config file when run via pnpm exec
• No npm-related warnings should be emitted
• The command should not fail due to stderr output unrelated to syncpack itself

Actual behavior

• syncpack spawns npx internally when loading JS/TS configs
• Because the process is already running under pnpm, npm receives pnpm-specific env config (e.g. npm_config_verify_deps_before_run)
• npm prints:

node.js/npx/tsx process failed swith stderr: npm warn unknown env config "verify-deps-before-run"

Contents of syncpack configuration file

module.exports = {
  semverGroups: [
    { dependencyTypes: ["peer"], range: "^" }
  ]
};

Optional comments

Problem is probably here: https://github.com/JamieMason/syncpack/blob/main/src/rcfile/javascript.rs#L75

let runner = if use_bunx { "bunx" } else { "npx" };

This causes npm to be invoked inside a pnpm process, which is not a supported or safe combination and leads to npm warnings being emitted on stderr.

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