Show HN: Cerulion – ROS 2-compatible robotics runtime with multi-process replay

Cerulion is an open-source, ROS 2-compatible runtime and development harness for AI-controlled robots. Its central claim is that robot behavior should be testable against real recorded runs before updated code reaches hardware: the system records inputs and execution context, then replays them through a graph and compares outputs. Nodes run in separate processes without changing the graph definition, while zero-copy messaging and remote access are intended to support deployment across machines. The project also describes safety limits enforced by the robot and tools for diagnosing failures. It is written in Rust, requires Rust 1.95 or newer to build nodes, and provides Linux and macOS releases; ROS 2 libraries are available for supported Linux distributions.

The quickstart demonstrates the verification workflow with a simulated laser scanner and obstacle-avoidance controller. The controller commands a forward speed of 0.3 when the path is clear and stops when an obstacle is closer than half a meter. After building and validating the graph, users run it for several seconds with recording enabled, then replay the recording against the unchanged code to get a passing verification. Changing the controller’s clear-path speed to 0.25 and rebuilding makes the same replay report a divergence and exit unsuccessfully, exposing changed behavior for review or CI checks. Recordings use MCAP, can remain local or be accessible through a signed-in account, and can be used offline after sign-in.