Stdio JSON-RPC plugin for out-of-process SDK clients such as Python deepseek_harness. HarnessSdkServer handles initialize → session/prompt → shutdown plus session and subagent notifications over JsonRpcLineTransport. This package owns the protocol; jsonrpc-agent boots the external cordis.yml that chooses the surrounding runtime. See the single-executable RFC for the distribution design.

Wiring

inject: ['agents']. The server gets or creates one agent per sessionId on session/prompt and demuxes subagent/end through the registry. If initialize.model lacks a registered adapter, it mounts dsh-llm-deepseek using $DEEPSEEK_API_KEY and $DEEPSEEK_BASE_URL; a config-registered adapter wins. Persistence, tools, and other adapters come from the surrounding cordis.yml.

Config

No cordis.yml keys. JsonRpcConfig.input, output, and exit are test-only runtime seams; production uses process stdio and process.exit.

stdout is the protocol

stdout carries only JSON-RPC frames. The loading config must omit stdout loggers; diagnostics go to stderr.

Shutdown and exit semantics

A shutdown request flushes its response, disposes the plugin fiber, then exits 0. Disposal idempotently shuts down every SDK-created agent to quiescence, detaches subscriptions, and closes the transport. Bare fiber disposal only stops serving; it does not exit. The app bin owns root disposal for stdin EOF (0), SIGTERM (0), and SIGINT (130).

Wire notes

initialize.serverInfo.name is the wire-stable deepseek-harness-sdk-runtime. Each session permits one in-flight prompt; overlap fails immediately, other sessions remain independent, and the session is reusable after settlement. Persistence roots and deployment persona remain in cordis.yml.

Model Experience

SDK user message

What the model sees: For each accepted session/prompt, the conversation model receives the caller-supplied contentBlocks verbatim as one user message in that SDK session. This package adds no system-prompt prose or tool schema; those come from the plugins in the surrounding cordis.yml.

Token effect: Data-dependent user-message tokens enter retained session history and are resent on later turns until another package compacts them. The JSON-RPC frames, session notifications, and server bookkeeping add zero model-context tokens.

Known Limitations and Deferred Work

The wire has no per-session close or prompt-cancel method — SDK-created agents remain live until process shutdown, and one accepted prompt runs to agent idle before that session accepts another.
stdout purity is deployment-enforced — a surrounding config can still load a stdout logger and corrupt the JSON-RPC channel; this plugin does not inspect or veto sibling loggers.
Automatic adapter mounting is DeepSeek-specific — initialize can reuse any pre-registered model adapter, but its only fallback mounts dsh-llm-deepseek.