[Security] Harden cloudflared installation against command injection

[gonzaloriestra]

User's Goal

Harden the cloudflared installation process against potential command injection vulnerabilities as per the security hardening guidelines.

Evaluation of the Solution

• Command Execution Safety: Replaced a call to child_process.execSync with system.exec in packages/plugin-cloudflare/src/install-cloudflared.ts. This ensures that arguments are passed as an array rather than a single shell-evaluated string, mitigating shell injection risks.
• Testing: Updated unit tests in packages/plugin-cloudflare/src/install-cloudflared.test.ts to mock the new system.exec utility. All tests in the package passed successfully.
• Security Best Practices: Added a comment explaining the security rationale for using exec instead of execSync.

Safety & Side Effects

• Backward Compatibility: The change is internal to the installation logic and does not affect the public API of the package.
• Regressions: The code was already asynchronous, so switching to the asynchronous exec is safe. All existing tests pass.
• Environment: No changes to package.json or tsconfig.json.

Testing performed

• Ran pnpm --filter @shopify/plugin-cloudflare vitest run (18/18 tests passed).
• Ran pnpm --filter @shopify/plugin-cloudflare exec eslint src/install-cloudflared.ts (No issues).
• Ran npx nx type-check plugin-cloudflare (Success).
• Ran npx knip --include-libs --workspace packages/plugin-cloudflare (No issues).

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PR created automatically by Jules for task 14450443894515539450 started by @gonzaloriestra

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