docs: rename core-data-structures/ to subsystems/

The folder is becoming the home of one-doc-per-subsystem pages (intro + data structures + cordis services/events), so the name must describe the whole contract, not just the type-vocabulary third of it. Mechanical rename rebuilt on current master: every inbound Markdown link, generator constant, website route, type-equiv manifest path, and spec expectation moves together; the zh sides of the notes whose prose names the folder are aligned (子系统) in the same change; touched bilingual pairs re-recorded; translation-prompt snapshot re-recorded (its example embeds development.md). Historical Agent Note slugs keep their dated filenames.
2026-08-09 01:27:09 +08:00
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+# Code Runtime
+
+English | [中文](code-runtime.zh.md)
+
+The code-execution seam — a [capability seam](../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md) whose interface ([dsh-code-runtime](../../packages/code-runtime/code-runtime), `ctx.codeRuntime`) runs one model-written program against host-provided async bindings and reports what it printed and returned. Code execution is **one optional capability**, not part of the agent-loop spine — so its vocabulary lives here, not in [core.md](core.md). Backends differ by execution substrate and source language, both readonly descriptors on the service; the worker-thread backend and tool-registry consumer are specified by the [Code Mode foundation](../../.agents/notes/implemented/feature/2026-06-15-code-mode.md) and [typed-return contract](../../.agents/notes/implemented/feature/2026-07-20-code-mode-typed-tool-returns.md).
+
+Source: [`packages/code-runtime/code-runtime/src/types.ts`](../../packages/code-runtime/code-runtime/src/types.ts)
+
+## The run: request in, result out
+
+A `CodeRunRequest` carries **everything the runtime acts on** — per the "explicit > implicit at package seams" rule, defaulting (time budgets, output caps) is the implementation's validated config, never a hidden `??` inside `run()`:
+
+```ts type-equiv
+/**
+ * One run: the program source plus everything the runtime acts on. Per the
+ * explicit-over-implicit convention, defaulting (time budgets, output caps)
+ * is the implementation's validated config — a request carries no optional
+ * tuning knobs for a hidden `??` to fill in.
+ */
+interface CodeRunRequest {
+  /**
+   * The program source, in the runtime's {@link ../index.ts | language}. It
+   * runs as the body of an async function: top-level `await` and `return`
+   * are available, and the completion value becomes
+   * {@link CodeRunResult.value}.
+   */
+  program: string
+  /** Host functions exposed to the program, one global object per namespace. */
+  bindings: CodeBindingNamespace[]
+  /**
+   * Abort the run: the runtime stops the program (hard, even mid-loop) and
+   * resolves with a {@link CodeRunFailure} of kind `'abort'`. In-flight
+   * binding calls are the CALLER's to settle — the runtime only stops asking.
+   */
+  signal?: AbortSignal
+}
+```
+
+The result reports an error as a **field**, never a rejection of `run()` — reporting a failed program is the caller's job, not an exception path (mirroring `BashExecutor.run`'s resolve-on-failure contract):
+
+```ts type-equiv
+/**
+ * The outcome of one run. An error is a FIELD on a resolved result, never a
+ * rejection of `run()` — reporting a failed program is the caller's job, not
+ * an exception path.
+ */
+interface CodeRunResult {
+  /**
+   * The program's completion value (its top-level `return`), when it ran to
+   * completion and the value crossed the runtime's lossless-JSON boundary.
+   * Invalid or over-limit completions fail the run instead of substituting a
+   * rendered string; a failed or value-less run leaves this absent.
+   */
+  value?: CodeJsonValue
+  /** Text the program emitted, in order, bounded only as part of the outer result. */
+  logs: string[]
+  /** Present iff the run failed; see {@link CodeRunFailure} for the taxonomy. */
+  error?: CodeRunFailure
+}
+```
+
+## Bindings: host functions as program globals
+
+Each `CodeBindingNamespace` becomes one global object of async callables inside the program (the Code Mode consumer passes one: `tools`). Arguments and resolutions must be lossless JSON and cross without a seam-level byte cap; the runtime may bridge them through structured clone. A namespace may declare a program-visible error class without making the runtime know the consumer's names: the runtime injects the real constructor and turns rejected calls into its instances. A runtime also treats binding names as hostile input (`__proto__` is an ordinary own property, never a prototype collision):
+
+```ts type-equiv
+/**
+ * Program-visible typed rejection for one binding namespace. The runtime
+ * injects a real error constructor under `name`; rejected member calls become
+ * its instances and expose the exact member name through
+ * `memberNameProperty`. Both strings are runtime data rather than knowledge
+ * of a particular consumer such as Code Mode.
+ */
+interface CodeBindingErrorClass {
+  /** Constructor global and resulting `Error.name`; same portable identifier rule as {@link CodeBindingNamespace.global}. */
+  name: string
+  /**
+   * Non-empty own property for the member name. The portable exclusion set is
+   * `RESERVED_ERROR_MEMBERS` plus dunder-form names (`__x__`, non-empty
+   * middle), enforced identically by every backend; any other name —
+   * identifiers or not — is accepted everywhere.
+   */
+  memberNameProperty: string
+}
+```
+
+```ts type-equiv
+/**
+ * A named group of {@link CodeBindingFunction}s the runtime exposes to the
+ * program as one global object (e.g. `tools`). Function names are arbitrary
+ * strings — a runtime must treat names like `__proto__` or `constructor` as
+ * ordinary own properties (null-prototype construction), never as prototype
+ * collisions.
+ */
+interface CodeBindingNamespace {
+  /**
+   * The global identifier the program sees. Must match the LANGUAGE-PORTABLE
+   * identifier subset `[A-Za-z_][A-Za-z0-9_]*` and no language's reserved
+   * words, so the same namespace list works against every backend regardless
+   * of `language` — a JS-only spelling like `$tools` is rejected by design,
+   * not just by the Python backend. Names that satisfy the identifier rule but
+   * name a backend-owned slot (`RESERVED_BINDING_GLOBALS`, e.g. `console`,
+   * `__dsh_main__`) are also refused everywhere; see its declaration for the
+   * exact set and why each entry is reserved.
+   */
+  global: string
+  /** The callable members, keyed by the exact name the program calls. */
+  functions: Record<string, CodeBindingFunction>
+  /** Optional program-visible typed rejection contract for this namespace. */
+  errorClass?: CodeBindingErrorClass
+}
+```
+
+```ts type-equiv
+/** A lossless JSON value transferable across the dependency-light code-runtime seam. */
+type CodeJsonValue = null | boolean | number | string | CodeJsonValue[] | { [key: string]: CodeJsonValue }
+```
+
+```ts type-equiv
+/**
+ * One host-side function exposed to the program as an async callable. The
+ * runtime bridges calls to it (possibly across a serialization boundary), so
+ * `args` and the resolution value MUST be lossless JSON. A runtime rejects a
+ * lossy or non-cloneable value with a descriptive error rather than corrupting
+ * the run. No seam-level byte cap applies to a binding resolution. A rejection
+ * of this function surfaces inside the program as a rejection of the
+ * corresponding call.
+ */
+type CodeBindingFunction = (args: unknown) => Promise<CodeJsonValue>
+```
+
+## Captured output and the failure taxonomy
+
+Logs are plain strings in emission order. The runtime captures the program's console and stream output, but channel and console-method metadata are not part of the seam because consumers render only the text. Implementations cap the serialized outer log-array plus completion-value or failure-message payload; fixed result-envelope syntax and consumer presentation whitespace are not part of that variable-payload ledger. Overflow is an explicit failure rather than in-band value substitution.
+
+Failure kinds are **orthogonal outcomes reported independently** (per [defensive-patterns](../defensive-patterns.md)): a budget expiry is not an exception, an abort is not a timeout, and a substrate death (e.g. OOM) is neither:
+
+```ts type-equiv
+/**
+ * Why a run failed. The kinds are orthogonal outcomes reported independently
+ * (per docs/defensive-patterns.md): a budget expiry is not an exception, an
+ * abort is not a timeout, and a substrate death is neither.
+ *
+ * - `'exception'` — the program threw or failed to parse/transform.
+ * - `'timeout'` — an implementation-owned budget expired; the message says which.
+ * - `'abort'` — {@link CodeRunRequest.signal} fired.
+ * - `'worker-exit'` — the execution substrate died without settling (e.g. OOM).
+ * - `'invalid-output'` — the completion value was not lossless JSON.
+ * - `'output-limit'` — the serialized outer logs/value/diagnostic exceeded the configured cap.
+ */
+interface CodeRunFailure {
+  /** The failure class (see the interface doc for each kind's meaning). */
+  kind: 'exception' | 'timeout' | 'abort' | 'worker-exit' | 'invalid-output' | 'output-limit'
+  /** Human-readable detail, suitable for feeding back to a model to self-correct. */
+  message: string
+}
+```
+
+## The service
+
+`CodeRuntime` (`ctx.codeRuntime`, abstract — defined in [`packages/code-runtime/code-runtime/src/index.ts`](../../packages/code-runtime/code-runtime/src/index.ts)) is `run(request)` plus two readonly descriptors: `language` (what the program must be written in — `'typescript'` and `'python'` are the well-known values, those `dsh-tools` presents, and only `'typescript'` has a published backend; a consumer generating language-specific presentation switches on it and fails loud on one it cannot present) and `isolation` (the execution substrate — `'worker-thread'`, `'process'`, `'container'`; a diagnostic label, **not a security claim**). Implementations must keep runs isolated from each other (no cross-run state) and dispose to quiescence: in-flight runs are terminated and awaited before teardown completes.