deepseek-harness/packages/sdk/protocol

@deepseek-ai/dsh-sdk-protocol

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The shared wire protocol for the DeepSeek Harness SDK runtime: one newline-delimited JSON-RPC 2.0 transport class plus the named request, result, and notification types both wire ends speak. The package root enumerates the protocol consumer interface; source modules are not exported as deep imports. The server side is the dsh-sdk-jsonrpc-server plugin; clients are dsh-sdk-client (TypeScript) and the Python SDK (which mirrors these shapes but does not import them). A pure library — no plugin, no Config, no registration.

Transport

JsonRpcLineTransport frames JSON-RPC 2.0 over caller-owned byte streams, one compact JSON frame per \n-terminated line. Frames with id and method are requests, id alone is a response, method alone is a notification; malformed JSON lines are ignored. start() attaches stream listeners, close() detaches them and rejects pending requests without destroying the streams. Missing request handlers answer -32601; handler rejections answer -32603 with the error message. An error response rejects the pending request() with JsonRpcResponseError, which preserves the wire code and optional data. JsonRpcTransportPeer is the outbound surface (request/notify) the server class is typed against.

Wire types

types.ts names every payload of the protocol served by HarnessSdkJsonRpcServer:

Direction	Method	Types
client→server	initialize	InitializeParams → InitializeResult
client→server	session/prompt	SessionPromptParams → SessionPromptResult (durable enqueue receipt)
client→server	shutdown	no params → {}
server→client	session.event	SessionEventNotification (every session in the runtime, unfiltered)
server→client	session.status	SessionStatusNotification (whole-agent running/idle transition)
server→client	subagent.started	SubagentStartedNotification
server→client	subagent.finished	SubagentFinishedNotification (in-process runs only)

HarnessSdkRequestMap and HarnessSdkNotificationMap index these by method name. SessionPromptResult.messageId identifies the queued UserMessage; it does not identify a later assistant message, turn ending, or prompt result. Clients combine the open-ended session.event stream with agent-wide session.status according to their own activity ownership. SubagentFinishedNotification.lastAssistantMessage contains the child's last non-empty assistant message or, when no such message exists, its accumulated assistant text; the field is absent when the child produced neither. InitializeParams.maxTokens is an optional positive safe integer that caps each conversation-model output for SDK-created agents and their in-process descendants; omission allows the selected adapter's exact-model default to apply, or otherwise preserves provider behavior. The notification payload types depend on SessionEvent (dsh-session), ContentBlock (dsh-llm), and SubagentStopReason (dsh-subagent) — the protocol streams full session-log envelopes, so the session vocabulary is part of the wire contract. serverInfo.name stays the wire-stable deepseek-harness-sdk-runtime.

Model Experience

None, as this package defines the client-facing wire protocol; the model-visible surfaces belong to the runtime plugins composed behind the serving dsh-sdk-jsonrpc-server entry.

KV Cache effect

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

Known Limitations and Deferred Work

• No protocol-version negotiation — the handshake carries only serverInfo.version (0.0.1, unvalidated by clients); pre-release stance, no compatibility promise.
• No cancel or session-close methods — a client abandons a turn by closing the runtime process; see the dsh-sdk-jsonrpc-server README.
• Server→client requests are dead capability — the transport supports them, but the server never sends one; the Python SDK's responder surface exists for future approval flows.