test-support/harness.mjs owns process, server, JSON, fixture, and plugin-runner helpers; provider helper files keep their APIs as thin wrappers. Guard fixtures write 0600 files and the CLI security test isolates XDG_CONFIG_HOME, so the suite passes on Linux. Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq