deepseek-harness/packages/code-runtime/code-runtime

@deepseek-ai/dsh-code-runtime

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The CodeRuntime (ctx.codeRuntime) defines WHAT a code runtime does — run one model-written program against a set of host-provided async bindings and report { value, logs, error? } — without saying HOW.

This package owns the Service Definition role of the capability (the bash trio is the template — see capability seams): providers subclass CodeRuntime and register the service; the Consumer is the tool registry's Code Mode, which generates the model-facing SDK and bridges tool dispatch — both specified in the Code Mode Agent Note, whose first provider is a Node worker-thread backend. The runtime knows nothing about tools or sessions: it is handed named async functions and a program string, and everything tool-shaped stays with the Consumer.

Service API (ctx.codeRuntime)

Member	Semantics
run(request)	Execute one program against the request's bindings. Resolves with an error FIELD for every program outcome — parse/transform failure, thrown exception, invalid completion, output overflow, budget expiry, abort, or substrate death (CodeRunFailure's orthogonal kind taxonomy); it rejects only for caller misuse of the Service Definition contract (e.g. a run submitted after disposal). The program runs as the body of an async function: top-level await/return work, and a lossless JSON completion becomes result.value.
language	Readonly descriptor: the source language run expects. 'typescript' and 'python' are the well-known values — those dsh-tools presents; only 'typescript' has a published backend. Informational, not gating — a consumer that generates language-specific presentation switches on it and fails loud on a language it cannot present.
isolation	Readonly descriptor: the execution substrate ('worker-thread', 'process', 'container'). A label for deployments and diagnostics, not a security claim.

Semantics every implementation must honor (contract details in the class JSDoc): binding calls bridge complete lossless-JSON arguments and resolutions with no seam-level byte cap; the program is treated as a hostile peer (arbitrary binding names are own properties, malformed traffic never crashes the host); no state survives between runs; disposal terminates in-flight runs AND awaits their exit before completing.

Vocabulary

CodeRunRequest (program, bindings, signal?) carries everything the runtime acts on — defaulting (time budgets and outer-output cap) is the provider's validated config, never a hidden ?? inside run(). bindings is a list of CodeBindingNamespaces (global + functions + optional errorClass), each exposed to the program as one global object of async callables returning CodeJsonValue, the service-local structural equivalent of canonical JsonValue that keeps this Service Definition package independent of sessions. An errorClass descriptor names a real program-global constructor and the own property that receives the rejected member name; runtimes remain independent of Consumer terms such as ToolCallError. CodeRunResult reports the lossless JSON completion value?, ordered logs: string[], and the error? (CodeRunFailure: kind + model-feedable message). See src/types.ts for the full contracts.

Binding-global and error-class names are language-portable: they must match the identifier subset [A-Za-z_][A-Za-z0-9_]* (no JS-only $) and clear the seam-exported exclusion sets, so one bindings list is valid against every backend regardless of its language. The package exports the contract every backend enforces — PORTABLE_RESERVED_WORDS (ECMAScript ∪ Python reserved words), RESERVED_BINDING_GLOBALS (backend-owned globals such as console), RESERVED_ERROR_MEMBERS and DUNDER_MEMBER (error-member exclusions) — so a name like $tools, lambda, or __dsh_main__ makes run() reject as seam misuse on any backend, not just some. See src/index.ts for the exact sets and rationale.

Model Experience

Indirectly, through Code Mode in dsh-tools, which exposes run_code and returns program logs, values, or failures as retained tool-result tokens.

KV Cache effect

No direct invalidation; the named consumer owns any request-prefix changes.

Known Limitations and Deferred Work

• run() is one-shot — logs arrive only on the resolved CodeRunResult; the seam exposes no streaming-log or progress API for a live program's output.
• A persistent REPL-style kernel is recorded future work — the no-state-between-runs contract stands until a persistent-kernel backend brings its own logging story (Code Mode Agent Note).
• Only the worker-thread backend ships — 'process'/'container' are declared well-known isolation values with no implementation; a hard security boundary awaits a container backend.
• Intermediate binding values have no byte cap — implementations remain subject to structured-clone cost and process memory, while a provider or executor may already have imposed its own acquisition bound.