deepseek-harness/packages/core/agent/README.md

dsh-agent

Agent interface, registry, and agent/* event vocabulary. Every plugin (UI, hooks, orchestrators) programs against the Agent handle defined here — it has zero loop dependency, so the loop is swappable.

Service: AgentRegistry (ctx key: agents)

Tracks live agents so UI, hook, and orchestrator plugins can find them without importing the concrete loop package.

Public API

• ctx.agents.register(agent: Agent): () => void — record an already-constructed agent. Disposed with the calling fiber.
• ctx.agents.get(id: AgentId): Agent | undefined
• ctx.agents.list(): Agent[]

Factory seam (creation)

Agent creation is provided by whichever plugin implements AgentFactory (phase 1: dsh-agent-loop), registered via setFactory. This keeps creation on the dsh-agent interface so consumers (UI, the ACP bridge) program against ctx.agents without depending on the concrete loop package.

• ctx.agents.setFactory(factory: AgentFactory): () => void — register the creation factory (the loop calls this on construction). Throws on a second factory; the slot clears on dispose.
• ctx.agents.create(options: CreateAgentOptions): AgentHandle — construct, start, AND register a new agent on a caller-supplied sessionId (with optional meta.cwd). Distinct from register (which only records). Throws if no factory is registered.
• ctx.agents.resume(options: ResumeAgentOptions): Promise<AgentHandle> — load a persisted session (session persistence) and resume an agent on it. Async; rejects if no factory is registered, or if the factory finds session persistence unconfigured.

AgentHandle = { agent: Agent; dispose(): Promise<void> }. The disposer is a capability — only the holder can tear this agent down. dispose() stops the loop, awaits its exit (quiescence — NOT just the disposed status flip), unregisters the agent, and removes its session from the store, in an order that captures the loop's final session/flush before the session is detached. ctx.agents.get(id) still returns a bare Agent — the handle is only for the OWNER that created it. The ACP bridge is the production consumer (one handle per session, disposed on disconnect/teardown); config-created agents are owned by the loop fiber and never need a handle.

Events

The full agent/* event taxonomy is declared via declaration merging in dsh-agent (not dsh-agent-loop), so plugins depend only on this package.

Lifecycle (emit)

• agent/created, agent/disposed — registration/deregistration
• agent/status — idle / running / disposed transition
• agent/queued — message entered inbox (source-resolved, steering flag)

Turn boundaries (emit)

• agent/turn-start, agent/turn-end (carries TurnEndReason)

Step boundaries are NOT mirrored as agent/* emits: a consumer that needs per-step boundaries reads the durable step/start/step/end session events (the session log is the live boundary feed). The turn boundaries stay as agent/* emits because the stdio UI needs the Agent handle (agent.id) at the boundary, which the session event does not carry. See the event-domain-semantics RFC.

Interception seams (waterfall)

• agent/request — mutate GenerateOptions before the model call (hooks, compaction, model switching, tool filtering)
• agent/step-result — post-process the assembled assistant message before tool dispatch (validates what the log records)
• agent/turn-continuation — override the continue/stop decision (force-continue /loop, force-stop budget guard)

Streaming + tool (emit)

• agent/stream-chunk — raw chunk from the model (token-level UI/log feed)
• agent/steering — steering content injected mid-turn
• agent/error — step/turn error

Agent interface (types.ts)

The handle every plugin programs against:

• agent.send(content, options?) — queue a message; starts a turn when idle
• agent.steer(content, options?) — steer a running turn (inject between steps); behaves like send when idle
• agent.inject(content, options?) — inject in-session context (context/message event); the next request sees it. Does not run the model. While a turn is open it joins that turn; while idle it is wrapped in a one-shot injection turn so every event stays turn-enclosed (the turn-enclosure invariant)
• agent.cancel(reason?) — cancel ALL pending work: clears the queued + steering FIFOs, aborts the in-flight step, and drops a turn about to start (the pre-step window) so a queued-but-not-started prompt never runs. A UI/ACP session/cancel maps to this. The single public stop primitive. Idle with nothing pending → a safe no-op.
• agent.whenIdle() — resolve once the agent reaches quiescence after settling out of running (idle → immediately; disposed → awaits the loop exit). A non-owner's quiescence-observation hook: it observes the work settling WITHOUT tearing the agent down. Teardown is separate — a lifecycle owner stops and unregisters via AgentHandle.dispose(), which awaits the loop exit directly.
• agent.session, agent.status, agent.options, agent.id

Extension points

• Agent creation: AgentLoop.create() is the concrete implementation (in dsh-agent-loop). Replace the loop by implementing Agent and registering via ctx.agents.register().
• Event listeners: all agent/* events are declared here — no dependency on the loop package needed.

What is NOT here (TODO)

• Sub-agent spawn/fork — seam on AgentLoop.create(), semantics deferred.