[Security] Fix command injection in treeKill utility

[gonzaloriestra]

WHY are these changes introduced?

treeKill in @shopify/cli-kit had a critical command injection vulnerability on Windows. The PID validation used Number.isNaN(pid) against a string, which always returns false for non-NaN string values, so malicious inputs like "1234; calc.exe" slipped through. The Windows branch then forwarded the value to child_process.exec via string concatenation, which spawns a shell and interprets the injected command.

WHAT is this pull request doing?

• Replaces the broken Number.isNaN PID check with a strict regex (/^\d+$/) so only digit-only strings are accepted.
• Switches the Windows taskkill invocation from child_process.exec (shell-based) to child_process.spawn with arguments passed as an array, eliminating shell interpolation.
• Adds packages/cli-kit/src/public/node/tree-kill.test.ts with regression coverage for malicious and valid PID inputs.
• Adds short security-focused comments at the validation and spawn sites.

How to test your changes?

treeKill is invoked when you quit shopify app dev (it tears down the dev process tree). Build the CLI, run a dev session against any sample app, and confirm a graceful shutdown:

pnpm install
pnpm shopify app dev --path <path-to-app>
# Inside the dev session, press 'q' (or Ctrl+C) and confirm the CLI exits cleanly.
# Then confirm no orphans were left behind (matches against full argv):
pgrep -fl 'app dev --path .*<path-to-app>' || echo "no orphan dev processes"

Then sanity-check the new PID validation directly. With a malicious PID it should refuse to spawn anything and surface the validation error. Run from the repo root against the built bundle:

pnpm nx build cli-kit
node -e "import('./packages/cli-kit/dist/public/node/tree-kill.js').then(({treeKill}) => treeKill('1234; calc.exe', 'SIGTERM', true, (err) => console.log(err?.message)))"
# Expect: pid must be a number

On Windows specifically, the taskkill invocation now uses spawn with array arguments instead of exec with string concatenation. Reviewers on Windows can confirm by running shopify app dev and quitting — the child tree should still terminate.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.