feat(subagent): add current-turn interrupt RPC

ctx.subagents.interrupt() stops one live continuable child's current turn
via Agent.cancel(cause, { keepInbox: true }) under either a human durable
parent address or an exact live ancestor Agent. Fire-and-return: admission
is synchronous, quiescence is not awaited. Pending inbox work, the
Activation, and published descendants are preserved; only a later waking
send resumes the parked FIFO queue. Absent, one-shot, and disposing
targets are accepted no-ops.

The new Host RPC subagent.interrupt calls only that primitive with user
authority — no catalog, history, persistence, or parent-registry lookup —
so a live child stays stoppable while its parent Agent is offline.

Refs #1535

.agents/notes/implemented/feature/2026-08-06-continuable-subagent-interrupt.i18n.yaml

@@ -0,0 +1,6 @@
+# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
+# side as of the last confirmed-consistent state. Both languages carry equal authority;
+# after editing either side, bring the other along and re-record with:
+#   pnpm run verify-translation-pairing --write .agents/notes/implemented/feature/2026-08-06-continuable-subagent-interrupt.md
+2026-08-06-continuable-subagent-interrupt.md: 729f1eb8259aa28aa771ed71872ebce9cadd4ed8
+2026-08-06-continuable-subagent-interrupt.zh.md: 15fe34d8b5e1d67623aabfe08710f341739e92e1

.agents/notes/implemented/feature/2026-08-06-continuable-subagent-interrupt.md

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+# Agent Note: Continuable subagent current-turn interrupt
+
+Status: implemented
+
+English | [中文](2026-08-06-continuable-subagent-interrupt.zh.md)
+
+## Problem
+
+A running continuable subagent could not be stopped without destroying it. The continuation manager cancels child Agents only inside whole-Activation teardown (settlement, drain, scoped drain), `send_message`/`subagent.prompt` only add work, and the Web composer's Stop button was deliberately limited to ordinary sessions. A human watching a continuable child burn tokens on a wrong path had no lever short of killing the parent tree, and when the direct parent Agent was offline the child was entirely untouchable even though its Activation stayed live. One-shot runs have holder-owned disposal and task-kill; continuable children had no analogous current-turn control.
+
+## Decision
+
+`ctx.subagents.interrupt(targetSessionId, authority)` stops only the live target's current turn. The manager primitive authorizes synchronously, calls the existing `Agent.cancel(cause, { keepInbox: true })`, and returns `void` — fire-and-return: the cancel signal is guaranteed issued, target quiescence is not awaited. Nothing else changes: no Activation disposal, no handle release, no descendant cascade, no inbox clearing, and no `AgentLoop` or `CancelOptions` change. Because `keepInbox` parks the pending queue at idle, an interrupt never auto-starts the next queued follow-up; only a later explicit waking send resumes the preserved FIFO order.
+
+Authority is a closed two-variant union, deliberately wider than delivery authority because stopping a turn is idempotent and delivers no content:
+
+- `{ kind: 'user', parentSessionId }` — a human presents the durable direct-parent address. The live target's `session.header.parentSession` must match; no live parent Agent, catalog read, or persistence access is involved, which is exactly what keeps a live child stoppable while its parent Agent is offline. Cancel cause `user`.
+- `{ kind: 'ancestor', agent }` — an exact live ancestor Agent (direct parent or deeper). The caller must be the registry's current entry for its id (stale callers are rejected even for absent targets), must not be the target itself, and must appear in the Activation's materialization-time `ancestry` WeakSet. Cancel cause `parent`.
+
+Targets are resolved only in the manager's process-local Activation map. An absent id — unknown, one-shot, or naturally settled — is an accepted no-op, which uniformly covers completion races and repeat requests without leaking durable-catalog information; a target whose disposal transaction is already open is likewise an accepted no-op after authorization. One-shot lifecycle (holder `dispose()`, task-kill) is untouched. `SubagentService.interrupt()` treats a manager-less composition as an accepted no-op rather than `CONTINUATION_UNAVAILABLE`, because without a manager no manager-owned live Activation can exist.
+
+The Host RPC `subagent.interrupt` takes the continuable `SubagentAddress` and returns `{ accepted: true }`. Its implementation calls only the core primitive with `user` authority — deliberately no `catalogChild()`, `listChildren()`, `sessionQuery`, or parent-registry lookup. A live target with a mismatched parent address maps to `subagent-unauthorized`; unexpected failures map to `internal` without leaking error text onto the wire.
+
+## Alternatives considered
+
+**Route human interrupts through `session.cancel`.** The generic session cancel requires an attached ordinary session and rejects subagent-owned sessions; widening it would entangle subagent authority rules with ordinary session routing. A subagent-domain RPC keeps the address-based authorization and the parent-offline guarantee explicit.
+
+**Await target quiescence and return the turn outcome.** Cancellation is cooperative, so quiescence is unbounded; holding the RPC (and a `ChildLock` slot) open invites timeouts and convoying against delivery and disposal. Acceptance-of-signal is the only fact the caller needs, and races (natural completion, disposal) already settle idempotently.
+
+**Reuse whole-Activation disposal for interrupt.** Disposal cancels without `keepInbox`, flushes, captures, and releases the handle — it destroys queued work and the child's residency. Interrupt is a control operation on one turn, not a lifecycle operation on the Activation.
+
+**Extend `send_message`/`followup` authority to ancestors while at it.** Delivery injects content into a conversation and is not idempotent; its exact-direct-parent authority stays unchanged. Only interrupt gets the wider ancestor and address-based user authority.
+
+**Auto-resume the parked queue after an interrupt.** Immediately starting queued follow-up B after aborting A would make the interrupt look ignored and steal the human's window to redirect the child. Parking until an explicit waking send keeps the stop observable and the FIFO order intact.
+
+## Consequences
+
+A human or ancestor can now stop a runaway continuable turn without losing the child, its queued work, or its running descendants; the cost is a deliberately weak postcondition (`accepted` means "signal issued", so a target may remain visibly `running` until it observes the signal) that clients must render honestly. The parked-queue rule means an interrupted child sits idle with retained work until someone sends a waking message — an intentional human-in-the-loop pause, not a scheduler defect. The Web Stop action and the model-facing `interrupt_agent` tool build on this primitive in the stacked follow-up PRs for issue #1535.
+
+## Testing
+
+Core coverage in `packages/subagent/subagent/tests/continuation.spec.ts` proves the durable `turn/end` abort, parked-then-FIFO-resumed queue, untouched descendant, both authority kinds with their cancel causes, self/sibling/stale/non-ancestor rejection, absent/one-shot/disposal-race no-ops, and the unchanged `keepInbox` loop behavior. Host coverage in `packages/host/apiproxy/tests` proves the RPC calls only the core primitive (no agents/catalog/history reads), the `subagent-unauthorized`/`internal` mappings, the wire schema's continuable-mode fence, and carrier round-trips.

.agents/notes/implemented/feature/2026-08-06-continuable-subagent-interrupt.zh.md

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+# Agent Note: Continuable subagent 当前轮次中断
+
+Status: implemented
+
+[English](2026-08-06-continuable-subagent-interrupt.md) | 中文
+
+## Problem
+
+一个正在运行的 continuable subagent 无法在不销毁它的前提下被停止。继续执行管理器只在整个 Activation 拆除（结算、drain、scoped drain）内部取消子 Agent，`send_message`／`subagent.prompt` 只能增加工作，而 Web composer 的 Stop 按钮被刻意限制在普通会话。人类眼看着一个 continuable child 在错误路径上烧 token，除了干掉整个 parent 树没有任何手段；当直接 parent Agent 离线时，即使 child 的 Activation 仍然在线，它也完全不可触及。一次性运行有持有方拥有的 disposal 和 task-kill；continuable child 没有对应的当前轮次控制。
+
+## Decision
+
+`ctx.subagents.interrupt(targetSessionId, authority)` 只停止在线目标的当前轮次。管理器原语同步完成鉴权，调用现有的 `Agent.cancel(cause, { keepInbox: true })`，然后返回 `void`——fire-and-return：保证取消信号已发出，但不等待目标静止。其余一切不变：不 dispose Activation、不释放 handle、不级联后代、不清空 inbox，也不改动 `AgentLoop` 或 `CancelOptions`。由于 `keepInbox` 让待处理队列停在 idle，中断绝不会自动启动下一个排队的 follow-up；只有之后一次显式唤醒发送才按保留的 FIFO 顺序恢复。
+
+授权是一个封闭的双变体 union，刻意比投递权限更宽，因为停止一个轮次是幂等的且不投递任何内容：
+
+- `{ kind: 'user', parentSessionId }`——人类出示持久化直接 parent 地址。在线目标的 `session.header.parentSession` 必须匹配；不涉及在线 parent Agent、目录读取或持久化访问，这正是 parent Agent 离线时在线 child 仍可被停止的原因。取消 cause 为 `user`。
+- `{ kind: 'ancestor', agent }`——一个确切在线的 ancestor Agent（直接 parent 或更深）。调用方必须是注册表中其 id 的当前条目（过期调用方即使目标不存在也被拒绝），不得是目标本身，并且必须出现在 Activation 物化时记录的 `ancestry` WeakSet 中。取消 cause 为 `parent`。
+
+目标只在管理器进程本地的 Activation map 中解析。不存在的 id——未知、一次性或已自然结算——是被接受的 no-op，统一覆盖完成竞态和重复请求而不泄露持久化目录信息；disposal 事务已打开的目标在鉴权后同样是被接受的 no-op。一次性生命周期（持有方 `dispose()`、task-kill）不受影响。`SubagentService.interrupt()` 把未绑定管理器的组合视为被接受的 no-op 而不是 `CONTINUATION_UNAVAILABLE`，因为没有管理器就不可能存在管理器拥有的在线 Activation。
+
+Host RPC `subagent.interrupt` 接收 continuable 的 `SubagentAddress` 并返回 `{ accepted: true }`。它的实现只以 `user` 授权调用核心原语——刻意不调用 `catalogChild()`、`listChildren()`、`sessionQuery` 或 parent 注册表查找。parent 地址不匹配的在线目标映射为 `subagent-unauthorized`；意外失败映射为 `internal`，不把错误文本泄漏到 wire。
+
+## Alternatives considered
+
+**让人类中断走 `session.cancel`。** 通用会话取消要求附着的普通会话并拒绝 subagent 拥有的会话；放宽它会把 subagent 权限规则缠进普通会话路由。subagent 域的 RPC 让基于地址的鉴权和 parent 离线保证保持显式。
+
+**等待目标静止并返回轮次结果。** 取消是协作式的，静止时间无上界；让 RPC（以及一个 `ChildLock` 槽位）保持打开会招致超时并与投递、disposal 形成排队。调用方需要的唯一事实是信号已被接受，而竞态（自然完成、disposal）本就幂等收敛。
+
+**复用整个 Activation 的 disposal 来做中断。** disposal 的取消不带 `keepInbox`，还会 flush、capture 并释放 handle——它销毁排队工作和 child 的驻留。中断是针对一个轮次的控制操作，不是针对 Activation 的生命周期操作。
+
+**顺手把 `send_message`／`followup` 权限扩展到 ancestor。** 投递向对话注入内容且不幂等；其确切直接 parent 权限保持不变。只有中断获得更宽的 ancestor 与基于地址的用户授权。
+
+**中断后自动恢复被暂停的队列。** 在中止 A 后立即启动排队的 follow-up B 会让中断看起来被忽略，并夺走人类重新引导 child 的窗口。暂停到显式唤醒发送为止，让停止可观察且 FIFO 顺序完整。
+
+## Consequences
+
+人类或 ancestor 现在可以停止一个失控的 continuable 轮次，而不丢失 child、其排队工作或正在运行的后代；代价是一个刻意保持弱的后置条件（`accepted` 表示"信号已发出"，目标在观察到信号前可能仍显示 `running`），客户端必须如实呈现。暂停队列规则意味着被中断的 child 会带着保留的工作停在 idle，直到有人发送唤醒消息——这是有意的 human-in-the-loop 暂停，不是调度器缺陷。Web 的 Stop 操作和面向模型的 `interrupt_agent` 工具在 issue #1535 的后续 stacked PR 中基于此原语构建。
+
+## Testing
+
+`packages/subagent/subagent/tests/continuation.spec.ts` 中的核心覆盖证明了持久化 `turn/end` 中止、队列先暂停后按 FIFO 恢复、后代不受影响、两种授权及其取消 cause、self/sibling/stale/非 ancestor 拒绝、absent/一次性/disposal 竞态 no-op，以及 `keepInbox` 循环行为不变。`packages/host/apiproxy/tests` 中的 Host 覆盖证明 RPC 只调用核心原语（不读 agents/目录/历史）、`subagent-unauthorized`／`internal` 映射、wire schema 的 continuable 模式围栏以及 carrier 往返。