According to NVIDIA, OpenShell enforces safety policies during agent runtime; teams can also add NVIDIA Sentry running on BlueField-4 for independent monitoring and enforcement.
The division of roles here is clear: one enforces policies within the runtime path, and the other provides monitoring and enforcement independent of the runtime path. But what specific mechanism "independent monitoring and enforcement" refers to, how Sentry and BlueField-4 work together, and what the capability boundaries and compatibility scope are—the source offers only general descriptions, no details.
There is also a retelling that claims OpenShell is an open-source secure runtime, but this claim comes from a secondhand retelling rather than NVIDIA's original text, so it can only be regarded as a source claim, not a confirmed fact.