deepseek-harness/packages/acp

@deepseek-ai/dsh-acp

The Agent Client Protocol (ACP) bridge: exposes the DeepSeek Harness coding agent as an ACP server over JSON-RPC stdio, so editors (Zed and other ACP clients) can drive it — streaming render, tool-call display, and resumable sessions.

It is a client-driver / UI plugin, the structured analogue of the readline stdio-chat plugin — NOT a loop change and NOT an ADR 0009 capability seam. It consumes the existing agent/* event taxonomy, the dsh-agent create/resume factory, and dsh-session-persistence.

Service / plugin

apply(ctx, config) — wires an AgentSideConnection (from @agentclientprotocol/sdk) to process.stdin/process.stdout and implements the ACP Agent method surface.

inject: ['agents', 'sessions', 'sessionPersistence'] — programs against the interface packages only (never dsh-agent-loop). sessionPersistence is required because initialize advertises loadSession: true.

Config

Key	Default	Meaning
model	—	Model name for created agents (must have a registered adapter).
systemPrompt	—	Per-agent system prompt.
agentName	deepseek-harness-acp	Server name reported in initialize.
agentVersion	0.0.1	Server version reported in initialize.

ACP method mapping

ACP method	Harness seam	Notes
initialize	static	negotiate protocolVersion; advertise text-only promptCapabilities and loadSession: true
session/new	ctx.agents.create({ sessionId, meta:{cwd} })	single-session MVP (a 2nd is rejected — RFC 011 lifts this); cwd must be absolute AND equal the server launch dir; additionalDirectories rejected; mcpServers ignored
session/load	ctx.agents.resume(...)	replays the persisted event log to the client as session/update — the USER side (user/message → user_message_chunk), assistant text/reasoning (assistant/chunk), and tool calls/results (tool/call + tool/result). The single-session slot is reserved (loading) BEFORE the async resume so a pipelined load/new can't leak a second agent; the PERSISTED header cwd is validated via a metadata-only list() BEFORE resume (not just the requested cwd), so a mismatch rejects without ever constructing an agent. After the async resume a closed re-check refuses to install a record if the bridge tore down mid-load
session/prompt	agent.send()	text-only; rejects image/audio and empty prompts; one in-flight prompt; settles on the OWNING turn's end (a turn that ends in error rejects the RPC)
session/cancel	agent.abort()	aborts a running step + settles the prompt cancelled (see limitation below)
session/update	session/event	agent_message_chunk (text-delta), agent_thought_chunk (reasoning-delta), user_message_chunk (load replay), tool_call/tool_call_update

Settle-exactly-once

A session/prompt resolves (or rejects) exactly once, keyed off the canonical session log (the session/event stream), NOT the agent/turn-start/agent/turn-end events. One listener captures the prompt's owning turn from the log's turn/start and settles on the matching turn/end — the one signal that always fires (closeTurn appends it unconditionally, even when a boundary emit throws and the agent/turn-end EVENT is skipped). A prompt settles only on ITS OWN turn (inflight.turn === turn/end.turn), so a stale turn/end for a previously-cancelled turn whose end arrives late can never settle the wrong prompt. A turn that ends error REJECTS the RPC with an internal error carrying the failure message (ACP has no error stop reason); every other reason resolves via the codec. As a fallback, when the agent settles to idle/disposed with a prompt still pending — e.g. a session/event listener registered before the bridge threw and starved the bridge's listener — an agent/status handler reconciles the prompt from the log (the owning turn's turn/end, or cancelled if the turn was torn down without one). An empty/whitespace prompt is rejected up front — it would queue no work, so no turn would start and the RPC would hang.

Disposal & disconnect

Teardown reaches quiescence: settle any pending prompt as cancelled, agent.abort(), then await agent.whenIdle() — the interface-level quiescence signal (NOT agent/status('disposed'), which fires before the driver exits). The same teardown runs on a client disconnect (conn.closed resolves when the editor quits / the transport EOFs), so a vanished client never leaves an orphaned running agent whose session/update writes are silently swallowed. The two paths are idempotent (each clears the record first).

Known limitations (tracked TODOs)

• TODO(rfc010-permission-gate) — the tools/execute permission gate (session/request_permission) is NOT implemented in this PR; tools run with the executor's full authority. The ownership WeakMap<Agent, sessionId> seam is laid down so the gate (and RFC 011 per-session permission ownership) can build on it. RFC 010 stays proposed until the gate lands.
• TODO(rfc010-cancel-prestep) — session/cancel (and teardown/disconnect) is honest RPC/UI cancellation plus best-effort abort: a running step is aborted, but a turn that is queued-but-not-yet-started (the gap before agent.abort() has an AbortController to signal) may still run to completion. This same window means disposal/disconnect can return while one short queued turn still runs, and a prompt accepted right after a pre-step cancel can be batched into the cancelled turn (the loop merges queued messages into one turn). A loop-level queue-aware cancel will close this; the single-in-flight-prompt rule bounds the worst case to one extra prompt.
• TODO(rfc010-agent-disposal) — the factory (ctx.agents.create/resume) returns no per-agent disposer, so teardown aborts+drains the agent but cannot individually unregister it; on a bare client disconnect (no host dispose) the idled agent lingers in ctx.agents until the host context disposes. Single-session-per-connection makes this benign today (a reconnect spins up a fresh context); RFC 011 adds the per-session disposal seam.
• cwd — only the server's launch directory is honored; a session/new.cwd (or a persisted session/load header cwd) that differs is rejected (RFC 010 § Deferred — no path from session cwd to the bash workdir yet).

stdout is the protocol

The JSON-RPC frames go on stdout, so this plugin MUST run in an example that loads no stdout logger (the console logger writes to stdout and would corrupt the frames). The guarantee is config-only — see examples/acp-agent (no console logger) and RFC 010 § Risks. A stderr exporter is fine for logging.

Running

yarn demo:acp boots examples/acp-agent (needs DEEPSEEK_API_KEY). Point an ACP client at it; for Zed, add to agent_servers:

{
  "agent_servers": {
    "DeepSeek Harness": {
      "command": "yarn",
      "args": ["demo:acp"]
    }
  }
}