# sim-lib-physics-runtime
In one line: Loadable composition of SIM physics surfaces without domain-policy duplication.
## What it gives you
Load exactly the scientific layers an application needs through the same SIM library mechanism used by every other domain. The runtime crate publishes discoverable layer-owned Cards while keeping solvers, certification policy, placement, persistence, and codecs in their proper owners. The contract keeps inputs, outputs, limits, and refusal cases explicit, so callers can compose the capability without acquiring unrelated host, transport, or product authority. Stable records make the result suitable for tests, inspection, and deterministic integration.
## Why you will be glad
- The public contract makes supported behavior, limits, and typed failures visible before integration.
- One owning crate prevents neighboring libraries from growing competing copies of the same policy.
- Deterministic records and checked tests keep adapters reviewable when implementations evolve.
## Where it fits
Within SIM, sim-lib-physics-runtime owns only the focused contract described above. Adjacent runtime libraries, platform adapters, codecs, and user surfaces can build around it while retaining their own policy. That boundary keeps the kernel small, avoids competing implementations, and lets this capability evolve without forcing unrelated components to change.