feat: add the code-execution capability seam (ctx.codeRuntime)

New group packages/code-runtime/ with the interface package
@deepseek-ai/dsh-code-runtime, per the Code Mode RFC: abstract CodeRuntime
service (run() resolves program failures as an error field, rejects only
for seam misuse), the CodeRunRequest/CodeBindingNamespace/CodeRunResult/
CodeLogEntry/CodeRunFailure vocabulary, and readonly language/isolation
backend descriptors. Registered in the tsconfig maps, packages/README,
architecture service map, and the doc-graph service-role classification;
catalogs regenerated.

The RFC's one forward path token to the worker package becomes an npm-name
mention until PR3 creates that directory (verify-package-paths is
drift-scoped: the now-existing group made the token checkable).

docs/architecture.md ceiling 1630 -> 1640: the doc gained a genuinely new
capability-service row; the row itself is already minimal.

packages/code-runtime/code-runtime/README.md

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+# @deepseek-ai/dsh-code-runtime
+
+The **code-execution seam**: an abstract `CodeRuntime` service (`ctx.codeRuntime`) defining 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 is the interface third of the capability (the bash trio is the template — see [capability seams](../../../docs/rfc/implemented/architecture/2026-06-13-capability-seams.md)): implementations 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 RFC](../../../docs/rfc/proposed/feature/2026-06-15-code-mode.md), whose first implementation 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, budget expiry, abort, substrate death (`CodeRunFailure`'s orthogonal `kind` taxonomy); it rejects only for caller misuse of the seam itself (e.g. a run submitted after disposal). The program runs as the body of an async function: top-level `await`/`return` work, and the completion value becomes `result.value` when it survives the serialization boundary. |
+| `language` | Readonly descriptor: the source language `run` expects (`'typescript'` is the well-known value). 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 to the caller's functions verbatim with structured-cloneable arguments/resolutions; 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, output caps) is the implementation's validated config, never a hidden `??` inside `run()`. `bindings` is a list of `CodeBindingNamespace`s (`global` + `functions`), each exposed to the program as one global object of async callables. `CodeRunResult` reports the completion `value?`, the ordered `logs` (`CodeLogEntry`: `console`/`stdout`/`stderr` source, console `level`, capped text), and the `error?` (`CodeRunFailure`: `kind` + model-feedable `message`). See `src/types.ts` for the full contracts.

packages/code-runtime/code-runtime/package.json

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+{
+  "name": "@deepseek-ai/dsh-code-runtime",
+  "description": "Abstract code-execution seam (ctx.codeRuntime) for the DeepSeek Harness",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "main": "lib/index.js",
+  "types": "lib/types/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./lib/types/index.d.ts",
+      "default": "./lib/index.js"
+    },
+    "./src/*": "./src/*",
+    "./package.json": "./package.json"
+  },
+  "files": [
+    "lib/index.js",
+    "lib/types/**/*.d.ts",
+    "lib/types/**/*.d.ts.map",
+    "src"
+  ],
+  "license": "BSD-3-Clause",
+  "peerDependencies": {
+    "cordis": "^4.0.0-rc.6"
+  },
+  "devDependencies": {
+    "cordis": "^4.0.0-rc.6"
+  }
+}

packages/code-runtime/code-runtime/src/index.ts

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+/**
+ * The code-execution seam (`ctx.codeRuntime`): an abstract service defining
+ * 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. Implementations subclass {@link CodeRuntime} and register
+ * themselves as the `codeRuntime` service; backends may differ by execution
+ * substrate (worker thread, separate process, container) and by source
+ * language, both declared as readonly descriptors. The design and its
+ * consumer (the tool registry's Code Mode) are specified in the Code Mode RFC
+ * (docs/rfc/proposed/feature/2026-06-15-code-mode.md).
+ *
+ * The split mirrors the bash seam (`BashExecutor`): the runtime knows nothing
+ * about tools or sessions — it is handed named async functions and a program,
+ * and everything tool-shaped stays with the consumer.
+ *
+ * @module @deepseek-ai/dsh-code-runtime
+ */
+
+import { Context, Service } from 'cordis'
+import type { CodeRunRequest, CodeRunResult } from './types.ts'
+
+export type {
+  CodeBindingFunction,
+  CodeBindingNamespace,
+  CodeLogEntry,
+  CodeRunFailure,
+  CodeRunRequest,
+  CodeRunResult,
+} from './types.ts'
+
+declare module 'cordis' {
+  interface Context {
+    codeRuntime: CodeRuntime
+  }
+}
+
+/**
+ * Abstract code-execution service. Subclass, implement {@link run} and the
+ * two descriptors, and load the subclass as a plugin — it registers as
+ * `ctx.codeRuntime` (one implementation per context; loading a second throws,
+ * cordis' standard duplicate-service behavior).
+ *
+ * Semantics every implementation must honor:
+ * - {@link run} resolves with an error FIELD for every program outcome —
+ *   parse/transform failures, thrown exceptions, budget expiry, abort,
+ *   substrate death ({@link CodeRunFailure}'s taxonomy). It REJECTS only for
+ *   caller misuse of the seam itself (e.g. a run submitted after disposal).
+ * - Binding calls bridge to the caller's {@link CodeBindingFunction}s
+ *   verbatim; arguments and resolutions must be structured-cloneable, and the
+ *   runtime treats the program as a hostile peer (arbitrary binding names are
+ *   own properties, malformed traffic is rejected or ignored, never crashes
+ *   the host).
+ * - Runs are isolated from each other: no state survives from one run to the
+ *   next through the runtime.
+ * - Disposal reaches quiescence: in-flight runs are terminated AND awaited
+ *   before the service's own teardown completes (no orphan substrate survives
+ *   `fiber.dispose()`).
+ */
+export abstract class CodeRuntime extends Service {
+  /**
+   * The source language {@link run} expects `program` to be written in, as a
+   * lowercase identifier. Informational, not gating — a consumer that
+   * generates language-specific presentation (typed SDK stubs, usage
+   * instructions) switches on it and fails loud on a language it cannot
+   * present. Well-known value: `'typescript'`.
+   */
+  abstract readonly language: string
+
+  /**
+   * The execution substrate, as a lowercase identifier. Informational, not
+   * gating — a descriptor so deployments and diagnostics can tell backends
+   * apart, not a security claim. Well-known values: `'worker-thread'`,
+   * `'process'`, `'container'`.
+   */
+  abstract readonly isolation: string
+
+  constructor(ctx: Context) {
+    super(ctx, 'codeRuntime')
+  }
+
+  /**
+   * Execute one program against the request's bindings and capture what it
+   * emitted. See the class doc for the resolution contract (error is a result
+   * field; rejection means seam misuse only).
+   * @param request - the program, its bindings, and the abort signal; the
+   *   request carries everything the runtime acts on, with no hidden defaults.
+   * @returns the run's outcome: completion value (when transferable), the
+   *   ordered log capture, and the failure (if any).
+   */
+  abstract run(request: CodeRunRequest): Promise<CodeRunResult>
+}
+
+export default CodeRuntime

packages/code-runtime/code-runtime/src/types.ts

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+/**
+ * Vocabulary types for the code-execution seam: what a caller hands a
+ * {@link ../index.ts | CodeRuntime} and what it gets back. Pure types — no
+ * runtime code lives here.
+ *
+ * @module @deepseek-ai/dsh-code-runtime/src/types
+ */
+
+/**
+ * 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 structured-cloneable; a runtime
+ * rejects a non-cloneable value with a descriptive error rather than
+ * corrupting the run. A rejection of this function surfaces inside the
+ * program as a rejection of the corresponding call.
+ */
+export type CodeBindingFunction = (args: unknown) => Promise<unknown>
+
+/**
+ * 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.
+ */
+export interface CodeBindingNamespace {
+  /** The global identifier the program sees (must be a valid JS identifier). */
+  global: string
+  /** The callable members, keyed by the exact name the program calls. */
+  functions: Record<string, CodeBindingFunction>
+}
+
+/**
+ * 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.
+ */
+export 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
+}
+
+/**
+ * One captured output entry, in emission order. `source` says which channel
+ * produced it: the program's `console` (shimmed by the runtime), or a stray
+ * write to the underlying stdout/stderr streams.
+ */
+export interface CodeLogEntry {
+  /** Which channel produced the text. */
+  source: 'console' | 'stdout' | 'stderr'
+  /** The console method used; present only when `source` is `'console'`. */
+  level?: 'log' | 'info' | 'warn' | 'error' | 'debug'
+  /** The captured text (possibly truncated by the implementation's caps, marked in-band). */
+  text: string
+}
+
+/**
+ * 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).
+ */
+export interface CodeRunFailure {
+  /** The failure class (see the interface doc for each kind's meaning). */
+  kind: 'exception' | 'timeout' | 'abort' | 'worker-exit'
+  /** Human-readable detail, suitable for feeding back to a model to self-correct. */
+  message: string
+}
+
+/**
+ * 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.
+ */
+export interface CodeRunResult {
+  /**
+   * The program's completion value (its top-level `return`), when it ran to
+   * completion and the value survived the runtime's serialization boundary;
+   * a non-transferable value is replaced by a string rendering, and a failed
+   * or value-less run leaves this absent.
+   */
+  value?: unknown
+  /** Everything the program emitted, in order (capped by the implementation). */
+  logs: CodeLogEntry[]
+  /** Present iff the run failed; see {@link CodeRunFailure} for the taxonomy. */
+  error?: CodeRunFailure
+}

packages/code-runtime/code-runtime/tests/service.spec.ts

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+import { describe, expect, it } from 'vitest'
+import { Context } from 'cordis'
+import { CodeRuntime } from '@deepseek-ai/dsh-code-runtime'
+import type { CodeRunRequest, CodeRunResult } from '@deepseek-ai/dsh-code-runtime'
+
+/**
+ * Minimal concrete runtime: records requests, "executes" by invoking every
+ * binding once in declaration order, and lets tests script the outcome. The
+ * seam package ships no implementation, so the contract is exercised through
+ * the smallest subclass that honors it.
+ */
+class StubRuntime extends CodeRuntime {
+  readonly language = 'typescript'
+  readonly isolation = 'in-process-stub'
+  requests: CodeRunRequest[] = []
+  nextResult: CodeRunResult = { logs: [] }
+
+  async run(request: CodeRunRequest): Promise<CodeRunResult> {
+    this.requests.push(request)
+    if (request.signal?.aborted) {
+      return { logs: [], error: { kind: 'abort', message: String(request.signal.reason) } }
+    }
+    for (const namespace of request.bindings) {
+      for (const fn of Object.values(namespace.functions)) {
+        await fn({ from: 'stub' })
+      }
+    }
+    return this.nextResult
+  }
+}
+
+async function setup() {
+  const ctx = new Context()
+  await ctx.plugin(StubRuntime)
+  const runtime = ctx.codeRuntime as StubRuntime
+  return { ctx, runtime }
+}
+
+describe('CodeRuntime service seam', () => {
+  it('registers as ctx.codeRuntime and serves the abstract API', async () => {
+    const { runtime } = await setup()
+    expect(runtime.language).toBe('typescript')
+    expect(runtime.isolation).toBe('in-process-stub')
+
+    const calls: unknown[] = []
+    const result = await runtime.run({
+      program: 'return 1',
+      bindings: [{ global: 'tools', functions: { probe: async args => void calls.push(args) } }],
+    })
+    expect(result).toEqual({ logs: [] })
+    expect(calls).toEqual([{ from: 'stub' }])
+    expect(runtime.requests).toHaveLength(1)
+  })
+
+  it('reports a failed run as an error field on a resolved result, never a rejection', async () => {
+    const { runtime } = await setup()
+    runtime.nextResult = {
+      logs: [{ source: 'console', level: 'error', text: 'boom' }],
+      error: { kind: 'exception', message: 'boom' },
+    }
+    const result = await runtime.run({ program: 'throw new Error("boom")', bindings: [] })
+    expect(result.error).toEqual({ kind: 'exception', message: 'boom' })
+    expect(result.value).toBeUndefined()
+  })
+
+  it('reports a pre-aborted signal as an abort failure', async () => {
+    const { runtime } = await setup()
+    const controller = new AbortController()
+    controller.abort('cancelled')
+    const result = await runtime.run({ program: 'return 1', bindings: [], signal: controller.signal })
+    expect(result.error).toEqual({ kind: 'abort', message: 'cancelled' })
+  })
+
+  it('is removed from the context when the providing fiber disposes (HMR safety)', async () => {
+    const ctx = new Context()
+    const fiber = await ctx.plugin(StubRuntime)
+    expect(ctx.get('codeRuntime')).toBeInstanceOf(StubRuntime)
+
+    await fiber.dispose()
+    expect(ctx.get('codeRuntime')).toBeUndefined()
+  })
+
+  it('rejects a second implementation in the same context (duplicate service)', async () => {
+    const { ctx } = await setup()
+    await expect(ctx.plugin(StubRuntime)).rejects.toThrow(/registered/)
+  })
+})

packages/code-runtime/code-runtime/tsconfig.json

@@ -0,0 +1,18 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "lib/types"
+  },
+  "include": [
+    "src"
+  ],
+  "references": [
+    {
+      "path": "../../../vendor/cosmokit"
+    },
+    {
+      "path": "../../../vendor/cordis"
+    }
+  ]
+}