Input and output rails as ordinary Ruby objects, returning passed, modified, or blocked, and reporting whether a rail actually reached the decision. Deterministic rails need no network at all; model-backed ones call any OpenAI-compatible endpoint through a provider abstraction that prefers a local proxy. Reads folders in the NeMo layout and executes a documented Colang 1.0 rail-flow subset in process. A NeMo folder is not drop-in. Optional client for teams who already run the Python server. Standard library only.