The jsonrpc plugin serves newline-delimited JSON-RPC over stdio so out-of-process SDK clients can drive harness agents. HarnessSdkServer owns the protocol methods and notifications; jsonrpc-demo supplies the surrounding cordis.yml application.

Wiring

inject: ['agents']. The server gets or creates one agent per sessionId. It forwards subagent completions only when the service-snapshotted lifecycle local flag is true; provider names, child ids, and durable lineage never establish locality. A registered adapter wins, an unowned deepseek route mounts dsh-llm-deepseek, and any other unowned provider fails initialization. Other capabilities come from the surrounding cordis.yml.

Config

maxTokensAsSuccess defaults to false. Set it to true for evaluation hosts that distinguish an accepted, token-limited agent result from an infrastructure failure. JsonRpcConfig.input, output, and exit are runtime-only transport seams; production uses process stdio and process.exit.

stdout is the protocol

Stdout carries only JSON-RPC frames. The deployment must not compose a stdout logger; diagnostics belong on stderr.

Shutdown and exit semantics

The plugin answers shutdown, disposes SDK-owned agents and subscriptions to quiescence, closes the transport, then exits with code 0. EOF and signal exits belong to the app bin, which disposes the root context. Unloading only this plugin stops serving without exiting the process.

Wire notes

initialize.serverInfo.name is the wire-stable deepseek-harness-sdk-runtime. A session accepts one in-flight prompt; overlap fails immediately, other sessions remain independent, and the session is reusable after settlement. session.finished reports that prompt's message-triggered turn outcome; later injection or plugin-owned zero-step turns still stream as session.event notifications but cannot replace the prompt status. Persistence roots and persona come from 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.

KV Cache effect

Append-only; newly visible content follows the reusable request prefix and does not invalidate existing KV-cache entries.

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.