The `code-runtime/` group provides program execution: a model writes one program that calls host-provided functions as ordinary async calls, and a runtime executes it in isolation and returns only what the program printed and returned. One package defines the shared capability (`ctx.codeRuntime`), a second executes TypeScript programs in a fresh Node worker thread, and a third owns the wire protocol between a Node host and a CPython subprocess for the Python backend. Every run is independent — no state carries from one program to the next — and failures come back as part of the result, so the caller can see why a program failed and feed that back to the model.
## Table of Contents
- [Packages](#packages)
- [Related documentation](#related-documentation)
- [Dev Note](#dev-note)
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## Packages
These three packages together provide program execution; each README describes what its part does.
| [`code-runtime/`](code-runtime/README.md) | Defines what a code runtime does: run one program against host-provided bindings and report what it printed and returned | `ctx.codeRuntime` |
| [`code-runtime-worker-thread/`](code-runtime-worker-thread/README.md) | Executes TypeScript programs, each in a fresh Node worker thread | registers `ctx.codeRuntime` |
| [`code-runtime-python/`](code-runtime-python/README.md) | Owns the fd-3 wire protocol between a Node host and a CPython subprocess, the Python backend's protocol layer | — |
Start with the subsystem reference for the service contract, then the PTC mode design that consumes this capability and the capability-seam model it follows.