The TypeScript client SDK for driving a DeepSeek Harness runtime as a subprocess over stdio JSON-RPC — the design twin of the Python SDK (deepseek-harness), sharing the same runtime peer, protocol, and layering: DeepSeekHarness is the high-level turns API, HarnessClient the lower-level protocol client. The package root enumerates the consumer interface: the two client layers, caller-facing types, and JsonRpcResponseError; source modules, normalization helpers, and subscription-delivery machinery are not consumer imports. A pure library: it registers nothing on a Cordis context; the runtime process it spawns is a complete harness whose composition its own cordis.yml decides.

Unlike the Python SDK, the launch spec is fully explicit (command/args): this package is for repo-adjacent TypeScript consumers — the dsh-subagent-dsh-sdk backend, tests, automation — which know which runtime they are launching. Bundled-runtime resolution (finding a packaged executable) remains the Python distribution's concern.

DeepSeekHarness

import { DeepSeekHarness } from '@deepseek-ai/dsh-sdk-client'

await using harness = new DeepSeekHarness({
  launch: { command: 'node', args: ['lib/bin.js', 'cordis.yml'] },
  provider: 'deepseek',
  model: 'deepseek-v4-flash',
  maxTokens: 49_152,
})
const result = await harness.run('say hi')
console.log(result.status, result.finalResponse)

The subprocess starts lazily on first use and stays owned by the instance across run() calls; close() (or await using) is required so the child is always reaped. start() memoizes the initialize handshake (the workspace cwd — resolved absolute before it crosses the wire — plus the provider/model route and optional positive maxTokens output cap); a failed handshake reaps the runtime and swaps in a fresh client, so a later call retries with a new subprocess (until close(), which is terminal). The cap applies to each root-agent request and is inherited by in-process descendants; compaction plugins own their separate summary limits. session(id?) opens a named or fresh session handle; run(input, { sessionId?, onNotification? }) sends one prompt turn and settles when the paired session.finished arrives, returning a TurnResult: status (ok/error as the deployment maps it), the structured reason (TurnEndReason), finalResponse (last assistant message text), root-session events, and raw notifications for that session plus descendants discovered from subagent.started, all in wire order. Model-level failure is a status: 'error' result, never a rejection; rejections mean transport loss, timeout, or protocol violation.

HarnessClient

The protocol client under the turns API: explicit start()/initialize()/prompt()/request()/close(), plus notification subscriptions. subscribe(filter?) returns a NotificationSubscription (awaitable next(), non-blocking tryNext(), async iteration); subscribeSessionTree(id) scopes to one session and the descendants discovered from subagent.started lineage edges — the runtime notifies for every session in its context, and scoping is client-side, exactly like the Python SDK. Error surfaces are typed and exported from this package: JsonRpcResponseError (wire error response, code/data preserved), RequestTimeoutError (a configured bound elapsed; there is no wire-level cancel, so the request keeps running server-side until close), SdkProtocolError (a response outside the documented protocol), TransportClosedError (the runtime is gone — message carries the exit code and a bounded stderr tail).

close() requests protocol shutdown (bounded by shutdownTimeoutMs, default 1000 ms), then walks a stdin-EOF → SIGTERM → SIGKILL ladder (disposeEofGraceMs default 6000, disposeGraceMs default 3000) until the process has actually exited. The ladder is private to this client: it runs outside any harness context, so it cannot ride the dsh-subprocess service — the seam's documented exception for SDK-managed transports. It is idempotent, and a closed client refuses reuse.

HarnessClientOptions.env replaces the child environment entirely when given (undefined inherits the parent's); callers own credential policy — scrubbedParentEnv from dsh-subprocess is the shared scrub base for isolation-minded launches.

Testing

Keyless unit tests drive a scripted fake runtime subprocess (tests/fake-runtime.ts, protocol-only, env-scripted) over real stdio: turn loop, session-tree scoping, timeout/death/malformed-response surfaces, and the dispose ladder. The SDK snapshot suite drives the real dsh-jsonrpc-agent runtime through this client keylessly via llm-replay, pinning the notification stream, the turn result, and the persisted logs; DSH_SNAPSHOT=record re-records against the live API.

Model Experience

None, as this is a client-process library; the model runs in the spawned runtime, whose experience is owned by the plugins its cordis.yml composes.

KV Cache effect

None; this package neither assembles nor sends a provider request.

Known Limitations and Deferred Work

No bundled-runtime resolution — callers name the runtime executable explicitly; packaged-executable discovery stays Python-side until a TypeScript distribution consumer exists.
No mid-turn cancel — the wire has no prompt-cancel method; abandoning a turn means closing the runtime (see the protocol's Known Limitations).
One in-flight prompt per session — a server-side rule this client surfaces as a JsonRpcResponseError; independent sessions run concurrently on one runtime.
Client→server notifications and server→client requests are unimplemented on both wire ends; the transport carries them for future approval flows.