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`sendReply` ignored `proto.write`'s `false` return, so a program resolving several large values in one `asyncio.gather` round encoded every reply in the same turn and queued all of them in fd 3's writable buffer. Binding resolution carries no seam-level byte cap to bound that, and the failure kills the host process rather than failing the run: measured on a 64 KiB-highWaterMark pipe, eight 4 MiB replies buffered 32.0 MiB at once against 0.0 MiB once paced. Replies now go through a queue that encodes and writes one frame at a time, awaiting `drain` when the pipe is full. The encode happens inside the loop, so a queued reply the run no longer needs is dropped by the `settled` check without ever being serialized. This was previously deferred on the grounds that serializing would narrow the seam's concurrency contract. That reasoning was wrong: the child matches each reply to its `call` by id from a pump that reads fd 3 continuously, so arrival order was never observable, and the bindings still run concurrently. Only the host's peak memory and the flush timing change. The README entry recording the deferral is removed and the Agent Note records the mechanism instead.
description, kind
| description | kind |
|---|---|
| Package map for the code-execution capability family: what program execution does for you, and which package owns each part. | package-group |
code-runtime/ — code-execution capability family
English | 中文
Summary
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
These three packages together provide program execution; each README describes what its part does.
| Package | Role | ctx key |
|---|---|---|
code-runtime/ |
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/ |
Executes TypeScript programs, each in a fresh Node worker thread | registers ctx.codeRuntime |
code-runtime-python/ |
Owns the fd-3 wire protocol between a Node host and a CPython subprocess, the Python backend's protocol layer | — |
Related documentation
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.
- Code runtime subsystem reference — request/result vocabulary, bindings, and the
ctx.codeRuntimecordis surface. - PTC mode Agent Note — how the tool registry presents
run_codeto the model. - Capability seams — the Service Definition / Service Provider / Consumer split this family follows.
Dev Note
Working context for maintainers — click to expand
None.