safeUnlink (ignores ENOENT), safeKill (ignores ESRCH), isProcessAlive
(extracted from cli.ts with Windows support), and json() Response helper.
All catches check err.code and rethrow unexpected errors instead of
swallowing silently. Unit tests cover happy path + error code paths.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>