The SDK server plugin (jsonrpc): mounting it serves a stdio JSON-RPC server that lets an out-of-process SDK client (e.g. the Python deepseek_harness package) drive DeepSeek Harness agents without touching Cordis. The client speaks newline-delimited JSON-RPC on the process stdin/stdout (HarnessSdkServer: initialize → session/prompt → shutdown, with session.event / session.finished / subagent.* notifications over JsonRpcLineTransport). The SDK-client analogue of the acp bridge, split the same way: this package is the protocol plugin, jsonrpc-agent is the app bin that boots a cordis.yml around it — which process serves this protocol is a config decision, not a hardcoded bin. This plugin is the serving face of the single-exe distribution plan — see docs/rfc/implemented/architecture/2026-07-10-single-file-executable-sdk-runtime-distribution.md.

Wiring

inject: ['agents'] — the server creates one agent per SDK sessionId (get-or-create on session/prompt). A local subagent's shared agent/session id supplies subagent.finished.childSessionId directly; the server verifies that the live child is owned by the exact delegating parent, then counts local starts by provider/id and that parent carrier because a continuation may reuse one child and the child may be disposed before a later subagent/end. The paired event carrier preserves parent correlation even when reused ids settle out of order. Runs from remote providers are not reported even when their parent-scoped run id collides with an unrelated local agent. The LLM seam is read opportunistically via ctx.get('llm') (not injected): when initialize.model has no registered adapter, the plugin mounts dsh-llm-deepseek for it (credentials from $DEEPSEEK_API_KEY / $DEEPSEEK_BASE_URL) — a config-registered adapter for the model wins. Everything else — persistence, the tool stacks, the adapter set — comes from the surrounding cordis.yml.

Config

No cordis.yml-settable keys. The JsonRpcConfig fields (input, output, exit) are runtime-only test seams so a spec can drive the server over in-memory streams without a subprocess or a killed test process; production always serves the process stdio and exits via process.exit.

stdout is the protocol

The process stdout this plugin runs in carries only JSON-RPC frames. The tree that loads it must load NO stdout logger (a console logger corrupts the frames) — the guarantee is config-only, same as the ACP bridge. Diagnostics go to stderr.

Shutdown and exit semantics

The plugin owns the PROTOCOL-level exit: a shutdown request is answered first (the response frame flushes), then the plugin disposes its own fiber — running the effect disposer: an idempotent server.shutdown() (every SDK-created agent disposed to quiescence, event subscriptions detached) plus transport.close() — and exits the process with code 0. Own-fiber disposal is deliberate: the request's server.shutdown() already flushed all SDK-owned session state, and the process exit that follows is the teardown of the rest of the tree. Process-level exits (stdin EOF → 0, SIGTERM → 0, SIGINT → 130) belong to the app bin, which disposes the whole root context. Fiber disposal WITHOUT a shutdown request (HMR-style unload) just stops serving — it never exits the process.

Wire notes

initialize.serverInfo.name is the wire-stable deepseek-harness-sdk-runtime (SDK clients key on it, independent of this package's name). A session accepts at most one in-flight session/prompt; an overlapping prompt for the same sessionId fails immediately through the standard handler-error response, while other sessions remain independent and the same session can be reused after the active prompt settles. Persistence roots and the deployment persona come from cordis.yml; the wire exposes only parameters the server applies.