fix(subagent): confirm steering request admission

packages/core/agent/README.md

@@ -64,8 +64,7 @@ The handle every plugin programs against:
 - `agent.reserveTurnAdmission()` — synchronously reserve the idle boundary before any queued waking prompt can claim its turn. An accepted prompt, including a same-tick pending wake, has right of way and makes reservation return `undefined`. Later sends keep their ordinary IDs, FIFO placement, and wakeup facts while held; `acceptsNextStep` remains false, `inject()` is not withheld, `whenIdle()` counts the reservation as activity, and the returned release is idempotent. This narrow coordination capability lets standalone durable operations such as manual compaction finish and flush before queued prompts derive from the session.
 - `agent.updateInbox(itemId, action)` — synchronously edits or removes one still-pending queued occurrence. Edit keeps its `MessageId`, `InboxItemId`, source, and FIFO position while replacing frozen content; remove emits the occurrence's terminal discard. Steering and claimed occurrences return `not-found`.
 - `agent.followup(input)` — the `next-turn`/wakeup preset of `send()`: queue an ordinary follow-up turn and wake the driver.
-- `agent.steer(input)` — the `next-step`/wakeup preset: during prompt admission or an open turn, stage steering for the next safe boundary without dispatching `agent/prompt-submit`; outside that acceptance window, delegate to a woken follow-up. Admission failure leaves staged steering for retry or a later admitted prompt, while cancellation or disposal may discard it.
-- `agent.trySteer?(input)` — an optional strict-steering capability implemented by the default loop. It atomically submits an identified message only while the current step still owns its final drain, returning `false` without accepting input during admission, between steps, or after that drain begins; cancellation and disposal can still discard accepted steering.
+- `agent.steer(input)` — the `next-step`/wakeup preset: submit one identified message and receive its `SteeringReceipt`. During prompt admission or an open turn, the message stages for the next safe request boundary without dispatching `agent/prompt-submit`; outside that acceptance window, it becomes a woken queued prompt. `receipt.outcome` resolves `admitted` with the turn and step only after the loop logs the message, captures it in immutable request history, and commits `step/start`. A turn-concluding tool result, broad cancellation, disposal, or pre-admission failure resolves it `rejected`; `cancel(..., { keepInbox: true })` and non-terminal routing preserve pending delivery. Reliable callers await the receipt, while best-effort UI steering may ignore it.
 - `agent.inject(input)` — the `next-step`/no-wakeup preset: append model-facing context without running the model; the next request sees a verbatim user-role message whose provenance is carried by the required `input.source`. During prompt admission or an open turn, injection waits in the outbox for the next safe boundary. Outside that acceptance window, it appends immediately without opening a turn; a context-only admission batch takes this fallback if admission closes without a turn, while context staged beside steering remains pending with it. Persistence reacts to `session/event` independently. Injection emits no `agent/inbox/*` event.
 - `agent.acceptsNextStep` — whether a `next-step` send would currently join prompt admission or the open turn. Use this narrower routing predicate when a caller must choose between steering and a fresh admitted prompt; `status === 'running'` also covers admission exit and turn settlement.
 - `agent.cancel(cause, options?)` — cancel the active turn and, unless `options.keepInbox`, ALL pending work. Callers must choose the `user | parent` cause explicitly; an active holder copies its discriminant into a detached frozen signal reason before aborting. An effective call emits `agent/cancel-requested` with the cause before clearing queued and steering work; dropped items are reported on `agent/inbox/discard`, and observers may synchronize state but cannot veto cancellation. `keepInbox: true` aborts the turn but preserves queued and steering items (no discard, and un-started work is not dropped). The same-process typed seam adds no runtime validation or compatibility fallback for untyped callers. Repeated active-turn cancellation is first-wins for the signal, and idle cancellation is a safe no-op with no notification. ACP maps to `user`, while in-process parent propagation maps to `parent`. The cause is runtime-only; durable `turn/end` stays coarse `aborted`.

packages/core/agent/README.zh.md

@@ -64,7 +64,7 @@ Agent *创建* 由实现 `AgentFactory` 的插件（`dsh-agent-loop`）提供，
 - `agent.reserveTurnAdmission()`：在任何已排队唤醒提示词认领其轮次之前，同步预留空闲边界。已获接纳的提示词拥有优先权，包括同一 tick 内仍在等待唤醒的项，此时预留返回 `undefined`。预留期间，之后发送的项保留其普通 ID、FIFO 位置与唤醒信息；`acceptsNextStep` 保持 false，`inject()` 不受阻塞，`whenIdle()` 将该预留计为活动，返回的释放函数可幂等调用。这项范围有限的协调能力使手动压缩（compaction）等独立持久操作能够在排队提示词从会话派生内容前完成并 flush。
 - `agent.updateInbox(itemId, action)`：同步编辑或移除一个仍处于待处理状态的 queued 入队项。编辑会替换已冻结的内容，同时保留其 `MessageId`、`InboxItemId`、来源与 FIFO 位置；移除会发出该项的终态 discard。steering 项和已被认领的项会返回 `not-found`。
 - `agent.followup(input)`：`send()` 的 `next-turn`／wakeup 预设：排队一个普通后续轮次并唤醒驱动器。
-- `agent.steer(input)`：`next-step`／wakeup 预设：提示词接纳期间或轮次打开时，为下一个安全边界暂存 steering，且不分发 `agent/prompt-submit`；该接收窗口之外则委托给会唤醒的后续轮次。接纳失败会保留暂存的 steering，以供重试或之后获准的提示词使用，而取消或 dispose 可能丢弃它。
+- `agent.steer(input)`：`next-step`／wakeup 预设：提交一条已有标识的消息，并取得其 `SteeringReceipt`。提示词接纳期间或轮次打开时，消息会为下一个安全请求边界暂存，且不分发 `agent/prompt-submit`；该接收窗口之外则成为会唤醒驱动器的排队提示词。只有循环记录消息、将其捕获到不可变请求历史并提交 `step/start` 后，`receipt.outcome` 才会解析为 `admitted`，并附带轮次与步骤。结束轮次的工具结果、广义取消、dispose（资源释放）或准入前故障会使其解析为 `rejected`；`cancel(..., { keepInbox: true })` 和非终止型路由会保留待处理投递。需要可靠投递的调用方应等待回执；尽力执行的 UI steering 可以忽略它。
 - `agent.inject(input)`：`next-step`／不唤醒预设：追加面向模型的上下文而不运行模型；下一次请求会看到一条逐字的 user role 消息，其来源由必填的 `input.source` 携带。提示词接纳期间或轮次打开时，注入会在 outbox 中等待下一个安全边界。该接收窗口之外，它会立即追加而不开启轮次；如果接纳结束却未开启轮次，仅含上下文的接纳批次会采用这一回退，而与 steering 一同暂存的上下文则会随其继续待处理。持久化独立地响应 `session/event`。注入不发出 `agent/inbox/*` 事件。
 - `agent.acceptsNextStep`：当前发送 `next-step` 时，是否会加入提示词接纳或已打开的轮次。当调用方必须在 steering 与新接纳的提示词之间选择时，应使用这一更窄的路由判定；`status === 'running'` 还涵盖接纳收尾与轮次结算阶段。
 - `agent.cancel(cause, options?)`：取消活动轮次，并在未设置 `options.keepInbox` 时取消全部待处理工作。调用方必须显式选择 `user | parent` 原因；活动持有者会在中止前把其判别字段复制为已分离、冻结的信号原因。有效调用会在清除排队与 steering 工作前，随原因发出 `agent/cancel-requested`；丢弃项在 `agent/inbox/discard` 上报告，观察方可以同步状态，但不能 veto 取消。`keepInbox: true` 会中止轮次，但保留排队与 steering 项（不丢弃，且不删除尚未开始的工作）。同进程类型化 seam 不会为无类型调用方添加运行时校验或兼容回退。重复取消活动轮次时，首个信号生效；空闲取消是安全空操作，不发通知。ACP 映射到 `user`，进程内父传播映射到 `parent`。原因只存在于运行时；持久 `turn/end` 保持粗粒度的 `aborted`。

packages/core/agent/src/types.ts

@@ -58,6 +58,20 @@ export type InboxAction =
 /** Result of applying an inbox action at the synchronous ownership boundary. */
 export type InboxActionResult = 'applied' | 'not-found'
 
+/** Final admission outcome for one call to {@link Agent.steer}. */
+export type SteeringOutcome =
+  | { readonly status: 'admitted'; readonly turn: number; readonly step: number }
+  | { readonly status: 'rejected' }
+
+/**
+ * Message-owned steering admission receipt. The outcome promise always
+ * resolves: synchronous input validation still throws from {@link Agent.steer},
+ * while lifecycle policy reports non-admission as `rejected`.
+ */
+export interface SteeringReceipt {
+  readonly outcome: Promise<SteeringOutcome>
+}
+
 /**
  * Options for the unified {@link Agent.send} primitive over the
  * (`target` × `wakeup`) matrix. Named presets: {@link Agent.followup}
@@ -225,26 +239,18 @@ export interface Agent {
   followup(message: UserMessage): void
 
   /**
-   * Submit steering during prompt admission or an open turn — the
-   * `next-step`/wakeup preset of {@link send}. It stages for the next steering
-   * checkpoint before a request or stop decision. If the activity fails before
-   * that boundary, the remainder stays staged without waking the agent; retry
-   * or a later prompt takes it. Outside that window steering falls back to a
-   * woken follow-up turn, while cancellation or disposal may discard pending
-   * steering.
+   * Submit steering with a message-owned admission receipt — the
+   * `next-step`/wakeup preset of {@link send}. During prompt admission or an
+   * open turn, the message waits in the steering FIFO until a committed step
+   * snapshots it; outside that window it enters the ordinary queued FIFO. The
+   * receipt resolves `admitted` only after the message joins that step's
+   * immutable request history, or `rejected` when terminal policy,
+   * cancellation, or disposal discards it first. A non-terminal turn close may
+   * leave it staged for a later admitted prompt without settling the receipt.
    * @param message - identified steering content and its producer provenance.
+   * @returns the receipt for this exact message's eventual admission outcome.
    */
-  steer(message: UserMessage): void
-
-  /**
-   * Atomically submit steering only while the current step still owns its final
-   * drain. Returns `false` without accepting the message during admission,
-   * between steps, or after the final per-step drain has begun. Cancellation or
-   * disposal may still discard previously accepted steering.
-   * @param message - identified steering content and its producer provenance.
-   * @returns whether the message entered the current step.
-   */
-  trySteer?(message: UserMessage): boolean
+  steer(message: UserMessage): SteeringReceipt
 
   /**
    * Append model-facing context without running the model — the

packages/core/agent/tests/agent.spec.ts

@@ -26,7 +26,7 @@ function stubAgent(rawId: string, overrides: Partial<Agent> = {}): Agent {
     send: () => {},
     updateInbox: () => 'not-found',
     followup: () => {},
-    steer: () => {},
+    steer: () => ({ outcome: Promise.resolve({ status: 'rejected' as const }) }),
     inject: () => {},
     reserveTurnAdmission: () => undefined,
     cancel() {},