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Subagent
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subagent seam：一个 agent（智能体）将工作委派给子 agent。与 bash 一样，它是一项可选能力，不属于 agent loop（智能体循环）主干，因此其词汇定义在此而非 core.md 中。但它在一个维度上与其他所有 seam 不同：同一上下文中可共存多个提供方实现，按名称注册（ctx.subagents），而 bash 只允许一个执行器。注册表的形状参照 LLM（大语言模型）适配器注册表，而非单服务的 bash 执行器。
接口：dsh-subagent（ctx.subagents + 下文词汇）。实现为三个兄弟包（package）：dsh-subagent-spawn、-fork、-acp；面向模型的消费方是 dsh-tool-subagent。提案与设计理由见 subagent Agent Note（agent 决策记录）。
源码：packages/subagent/subagent/src/types.ts
两类能力，两种发现方式
提供方通过一个静态描述符公布其启动时特性，服务在 run 存在之前即行检查；如果请求依赖提供方不具备的特性，会被大声拒绝（SubagentError('UNSUPPORTED_CAPABILITY')），绝不会被接受后静默忽略。运行时特性（steering（中途引导）、恢复）则是 SubagentRun 上的可选方法——方法的存在即为能力，TypeScript 的类型收窄即为发现机制。
/**
* Which START-TIME features a provider supports. Checked by the service before delegating to
* {@link SubagentProvider.start}: a request that needs a capability the chosen provider lacks
* is rejected with a typed error rather than accepted-then-ignored (the "fail loud, no silent
* degradation" rule). These static flags cover features needed before a run exists; runtime
* capabilities such as steering and resume are optional {@link SubagentRun} methods whose presence
* is the capability. Each flag corresponds one-to-one to a {@link SubagentStartRequest} option:
* `depthLimit` to `maxDepth`; the other names match.
*/
interface SubagentCapabilities {
readonly outputSchema: boolean
readonly depthLimit: boolean
readonly toolFilter: boolean
readonly persona: boolean
}
启动请求
工具层根据模型输入和自身配置构建此请求；服务在 start 之前针对指定提供方进行校验。必填的 parent 提供会话 cwd、谱系与委派深度。可选的 output schema、depth、工具过滤器和 persona 需要对应的能力 flag 匹配。不支持的 schema 在启动时即失败；进程内后端将 filter 和 persona 的作用域限定在子 agent 创建阶段，并通过强制 capture 工具实现所支持的 object-rooted schema。
/**
* What a caller asks for when starting a subagent. The tool layer builds this
* from the model's `{ description, prompt }` plus its own config; the service
* validates {@link SubagentCapabilities} against the named provider, then
* passes it to {@link SubagentProvider.start}.
*/
interface SubagentStartRequest {
/** Content delivered as the child's user message. */
readonly prompt: ContentBlock[]
/**
* The spawning agent. In-process providers derive workspace, lineage, and
* delegation depth from its durable session state. ACP reads only its cwd,
* and only when no deployment `cwd` override is configured.
*/
readonly parent: Agent
/**
* Cancellation signal from the spawning context (the tool's `exec.signal`).
* This is the canonical cancellation channel both before and after startup:
* a provider rejects `start()` after cleaning partial resources when it
* fires before publication, and cancels a published child when it fires
* afterward.
*/
readonly signal: AbortSignal
readonly agentOptions?: AgentOptions
/**
* Object-rooted JSON Schema within `assertObjectJsonSchema`'s enforced subset. Start rejects
* unsupported schemas or providers without the capability. Data must be plain host-realm JSON;
* a successful child returns the matching value as {@link SubagentResult.structured}.
*/
readonly outputSchema?: ObjectJsonSchema
/**
* Optional absolute delegation-depth cap for the child being started: its
* computed depth must be less than or equal to this non-negative safe
* integer. Requires {@link SubagentCapabilities.depthLimit}; rejected at
* start otherwise.
*/
readonly maxDepth?: number
/**
* Optional child tool scoping. Requires {@link SubagentCapabilities.toolFilter};
* rejected at start otherwise. In-process backends apply it as a scoped
* `tools.restrict()` in the child's creation window: the named tools vanish
* from the child's prompt AND refuse to execute (one visibility), with loud
* unknown-name validation.
*/
readonly toolFilter?: ToolRestriction
/**
* Optional per-child persona. Requires {@link SubagentCapabilities.persona};
* rejected at start otherwise. In-process backends register it as a scoped
* `deployment:persona` section on the child, SHADOWING the deployment's
* persona for this child alone — same template semantics as the deployment
* persona (strict `{{…}}` interpolation against the registered variables).
*/
readonly persona?: string
}
signal 是就绪前后唯一的取消通道。subagent 组合控制 Agent Note规定 persona、live 全局工具过滤、绝对深度以及「可见性而非权限」的设计理由。
终态结果：SubagentResult
一次 run 的最终产出，由 SubagentRun.result resolve。structured 仅在请求了 outputSchema 且成功满足时才存在；请求 schema 不保证一定能得到它，当子 agent 失败或结束时未产出有效 capture 时，提供方可能返回 stopReason: 'error'。非 completed 的 stopReason 意味着 output 可能不完整——消费方将其映射为 isError 的工具结果，而非将部分输出报告为成功。
/**
* The terminal outcome of a subagent run, resolved by {@link SubagentRun.result}.
*/
interface SubagentResult {
/** The child's final assistant output (the last assistant message's content). */
readonly output: ContentBlock[]
/**
* The structured result after a requested `outputSchema` was successfully
* satisfied. Requesting a schema does not guarantee presence: a provider can
* end with `stopReason: 'error'` when the child fails or finishes without a
* valid capture. Shape is validated against the request schema by the
* provider; `unknown` here because the seam is schema-agnostic.
*/
readonly structured?: unknown
/** Why the run ended. A non-`completed` reason means `output` may be partial. */
readonly stopReason: SubagentStopReason
}
SubagentStopReason 是一个可合并扩展的派生联合类型——后端可以添加变体，因此消费方应对已知 case 分支处理，将未知的终态原因视为失败：
/**
* Why a subagent run ended. Merge-extensible (a backend may add variants);
* consumers branch on the known cases and fall through `default`. The known
* cases mirror the harness turn-end vocabulary so the tool layer can map a
* non-`completed` result to an `isError` tool result.
*/
interface SubagentStopReasonMap {
/** The child finished its turn normally. */
completed: 'completed'
/** Cancelled through the request signal or disposal. */
aborted: 'aborted'
/** Model or transport failure. */
error: 'error'
/** The child hit its token ceiling before finishing. */
'max-tokens': 'max-tokens'
/** The child declined the task. */
refusal: 'refusal'
}
活跃 run：SubagentRun
SubagentRun 是消费方持有的、指向一个就绪子 agent 的句柄。消费方 await result 并始终 dispose（资源释放）该 run，直至其完全停稳。子 agent 失败时以非 completed 的 stop reason resolve；只有不可表示的基础设施故障才会 reject。可选的 sendMessage 和 resume 方法通过自身的存在来公布运行时能力。
/**
* Child handle returned only after readiness. Consumers await {@link result} and must always
* {@link dispose} to cancel remaining work and reach quiescence. Optional methods are runtime
* capability discovery; narrow their presence before calling.
*/
interface SubagentRun {
/**
* Parent-scoped run id. For a local run, this MUST equal the published child
* session id, whose `parentSession` records `request.parent.session.id`; a
* remote provider mints an id unique in the parent namespace.
*/
readonly id: SessionId
/**
* The exact published in-process child, or `undefined` for a remote run.
* When present, its id is {@link id}; the provider retains no ownership
* implication beyond the run's ordinary {@link dispose} contract.
*/
readonly localAgent: Agent | undefined
/**
* Resolves with the child's terminal {@link SubagentResult} when the run
* settles. Does NOT reject on a child-level failure — a model/transport
* failure resolves with `stopReason: 'error'` so the consumer maps it to an
* `isError` tool result. Rejects only on an infrastructure fault the seam
* cannot represent as a stop reason.
*/
readonly result: Promise<SubagentResult>
/**
* Cancel remaining work, reach child quiescence, and release resources.
* Idempotent.
*/
dispose(): Promise<void>
/**
* OPTIONAL (steering capability): send additional content to the running
* child between steps. Present only on providers that support live steering.
*/
sendMessage?(content: ContentBlock[]): void
/**
* OPTIONAL (resume capability): send a follow-up task to a settled child,
* continuing its session, and return a fresh run for the continuation.
*/
resume?(content: ContentBlock[]): Promise<SubagentRun>
}
本地 run 必须在 start() fulfill 前发布一个普通子 agent/会话，将该子会话 id 作为 SubagentRun.id 返回，以 localAgent 暴露确切子 agent，并在子 agent 的 parentSession header 中记录 request.parent.session.id。运行时所有权可以把子 agent 放在 parent、提供方或 root 作用域下。远程提供方则返回 parent 作用域的生命周期 id 与 localAgent: undefined。
提供方 seam：SubagentProvider
每个提供方是一个具名的子 agent 传输层，多个提供方可以共存。服务在 start() 之前校验请求的启动时能力。inheritsParentContext 仅描述对话种子注入（fork：true；spawn 和 acp：false），使消费方能生成准确的面向模型的措辞，而不暗示继承了工具、服务或权限。
/**
* One registered transport for running child agents. Providers are trusted
* same-process implementations; callers treat descriptors and returned values
* as borrowed immutable data.
*/
interface SubagentProvider {
/** Unique registry name (e.g. `spawn`, `fork`, `acp`). */
readonly name: string
/** The start-time features this provider supports (see {@link SubagentCapabilities}). */
readonly capabilities: SubagentCapabilities
/**
* Whether the child sees the parent's completed-turn prefix. This is descriptive, not a
* service-validated start capability: the model-facing tool derives truthful wording from it.
* It says nothing about tool registration, injected services, or authority inheritance.
*/
readonly inheritsParentContext: boolean
/**
* Establish a child and return its handle only after publication. The
* service has already validated that every requested start-time capability
* is supported, so an implementation may assume e.g. `request.maxDepth` is
* honorable when present. If setup fails or `request.signal` aborts before
* fulfillment, the provider owns and cleans all partial resources before this
* promise rejects. Ownership transfers to the caller only on fulfillment.
*/
start(request: SubagentStartRequest): Promise<SubagentRun>
}
start() 仅在 run 就绪时 fulfill。服务铸造唯一 runId，从提供方的确切 localAgent 快照 local，观察结果，emit subagent/start，并返回同一个 run；rejection 意味着提供方已清理，且不会 emit 生命周期事件对。配对的 subagent/end 携带相同标识与最终输出或基础设施失败。两个事件都仅用于观察，每个 listener 异常都会被独立隔离。
进程内后端：深度与种子
spawn 和 fork 后端通过 parent.ctx 创建一个普通 agent，将取消信号传入核心创建流程，并通过 AgentHandle 进行 dispose。移除提供方会阻止新的 start，但不会撤销已接受的 run。每个子 agent 获得一个新的扁平作用域，而非继承父级注册。深度与 fork 种子注入复用既有的 agent 和会话词汇：
- 委派深度由持久
SessionHeader.delegationDepth与可合并扩展的运行时字段AgentOptions.subagentDepth共同表示；缺失表示顶层深度为零，存在的较大值具有权威性。两个字段都归该 seam 所有——循环既不设置也不读取它们——因此进程内子 agent 会持久保存 parent 深度 + 1，恢复无法降低深度，而且每次 start 都会拒绝超出安全整数域、或高于已定义绝对request.maxDepth上限的派生深度。 - Fork 种子注入使用
CreateAgentOptions.seed（一个SessionEvent[]前缀，经由AgentLoop.createAgent→ctx.sessions.prepare({ seed })传递，与resume使用的原语相同）。fork 后端传入父级日志的一段平衡的已完成轮次前缀——父级事件直到并包括其最后一个turn/end——因此种子从 0 连续，invariants 回放可以接受它（进行中的、未平衡的轮次被排除在外）。