# DeepSeek Harness Python SDK

English | [中文](README.zh.md)

Python subprocess SDK for driving DeepSeek Harness over JSON-RPC stdio. The
runtime inherits normal DeepSeek Harness environment variables such as
`DEEPSEEK_BASE_URL` and `DEEPSEEK_API_KEY`, so callers can use real model
endpoints directly or point those variables at a local proxy.

Install the `deepseek-harness-sdk` distribution from PyPI; the import module remains `deepseek_harness`:

```sh
python -m pip install deepseek-harness-sdk
```

Installing `deepseek-harness-sdk` installs the exact same-version `deepseek-harness-runtime-bin` platform wheel. The normal entry point therefore needs no executable argument:

```py
from deepseek_harness import DeepSeekHarness

with DeepSeekHarness() as harness:
    result = harness.run("Say hi.")
```

`DeepSeekHarness` keeps its lazily started runtime subprocess for reuse across calls. Use it as a context manager, as above, or call `close()` explicitly when finished.

By default, the SDK launches the bundled single-file `dsh-jsonrpc-agent` executable from the `deepseek-harness-runtime-bin` package and injects that package's default configuration (the stdio JSON-RPC server, agent core, preloaded DeepSeek adapter, JSONL session persistence with an explicitly composed semantic checkpoint policy, local bash) via `DSH_CORDIS_CONFIG`. To run a plugin composition of your own, keep the `@deepseek-ai/dsh-jsonrpc` entry in the config and pass the Cordis config path.

```py
from deepseek_harness import DeepSeekHarness

with DeepSeekHarness(
    provider="deepseek-official",
    model="deepseek-v4-flash",
    max_tokens=49_152,
    cordis="examples/jsonrpc-agent/cordis.yml",
) as harness:
    result = harness.run("Make the requested code change.")
```

`provider` selects a provider route registered by the chosen Cordis composition; `model` is the model id resolved by that adapter. `max_tokens` is an optional positive per-request output-token cap for the root agent and its in-process descendants; omission leaves the provider default in control. Compaction summaries keep the separate limit configured by their compaction plugin. The bundled default composition registers `deepseek-official`. A custom composition can mount `llm-pi-ai`, configure provider-specific credentials/endpoints there, and select any provider/model present in pi-ai's installed catalog.

The [Python SDK tutorial](../../docs/user/guide/python-sdk.md) uses a complete standalone Cordis file to demonstrate installation, direct SDK usage, and runs without the Web UI.

`Session.run()` owns an activity interval from its prompt's durable inbox receipt through the next whole-agent idle and returns `RunResult(session_id, final_response, finish_reason, events, notifications, session_root)`. `final_response` is the last committed root-session assistant text in the interval. `finish_reason` is the `kind` of the last root-session `turn/end` in the interval, such as `completed`, `max-tokens`, or `error`, and is `None` when no turn ended. Both fields describe the owned interval rather than an output or ending causally assigned to the prompt. Steering, injected context, and other queued work may contribute before idle.

`HarnessClient` retains discovered subagent ancestry for the lifetime of the runtime process. During each `Session.run()`, `RunResult.notifications` and `on_notification` receive the root session and all known descendant notifications in wire order, including nested subagent lifecycle and session events. `RunResult.events` contains root-session events only, so descendant messages cannot replace the root response. The low-level `session_prompt()` returns the queued `MessageId` immediately; callers that bypass `Session.run()` own any later activity boundary themselves.

The same behavior can be selected for the runtime subprocess with `DSH_CORDIS_CONFIG`. The injection lives in `HarnessClient.start()`, so the low-level client's default launch gets it too: when the launch resolves to the bundled runtime and neither `cordis` nor a non-empty `DSH_CORDIS_CONFIG` is set (the runtime treats an empty value as absent, and so does the injection check), the bundled default configuration is used; an explicit `runtime_bin`, `bridge_bin`, or `launch_args_override` disables the injection entirely. See the [sdk-runtime README](../sdk-runtime/README.md) for the runtime carriers (production exe vs dev-only node closure) and how to obtain them.

`cwd` and `runtime_cwd` are resolved to absolute paths before subprocess launch, environment injection, and the wire handshake. The public API exposes only applied options: deployment persona and persistence belong in `cordis.yml`, while `session_root` remains the high-level convenience that sets `DSH_SESSION_ROOT`.