sidecar
a small helper process that runs beside a main program
A sidecar is a separate process that runs alongside the main application and handles one supporting job — here, checking each tool call before it runs. Running it separately means the check can be added without rewriting the agent, and the two can be updated independently. The alternative is running the same logic in-process, inside the agent itself.
Think of it as
A checkpoint booth placed just outside a building's one exit: everyone still leaves through it, but it was added without rebuilding the building.
Ideas that use this term