feat(subagent): deliver continuable child settlement to parents

A continuable child that stopped without reporting — an error, a token
ceiling, cancellation, teardown — left its parent nothing to act on.
The continuation manager now delivers an unconditional settlement
notice to the durable direct parent before releasing ownership, folding
consumed work (foldConsumedWork supersedes findLastMessageTurnEnd) so a
claimed-but-unrun prompt reads as aborted rather than completed, waking
an idle parent, steering a busy one, and never waking a closing tree.

packages/subagent/tool-subagent/README.i18n.yaml

@@ -2,5 +2,5 @@
 # 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 packages/subagent/tool-subagent/README.md
-README.md: ac3ec0563cce9128608ca31860b034a103dc1a3a
-README.zh.md: d64831d7cf64800ad3307ce6cb7f294500a0a6f0
+README.md: a46300cc5dffcbc420ed9525d8f081c670771294
+README.zh.md: 985d33beb2ac7de60527b457c4786a0257232611

packages/subagent/tool-subagent/README.md

@@ -10,7 +10,7 @@ Each plugin instance binds one `provider` to one `toolName`; the model receives
 
 A foreground call passes the execution signal through startup and execution, awaits `run.result`, and always awaits `run.dispose()` before returning. Only `completed` returns the canonical `{ kind: 'foreground', runId, output: JsonValue[] }`, rendered as the same final text; abort, refusal, token limit, and other failures become errored tool results whose message appends the child's preserved partial text (the `SubagentResult.output` selection) after the stop-reason headline, so a truncated answer is never reported as success yet never silently lost. If result collection and disposal both reject, the errored result preserves both diagnostics.
 
-With `run_in_background: true`, `backgroundMode` selects the route. `one-shot` registers a plain parent-owned Task and returns canonical `{ kind: 'background', taskId }`, rendered as `started background subagent task <id>`, even when the provider supports continuable children; generic task tools own its later status, collection, cancellation, and notices. `continuable` requires a provider with the `prepareContinuable` capability, calls `ctx.subagents.startContinuable()`, and returns `{ kind: 'continuable', subagentId }`, rendered as `started subagent <childId>`. The continuable route resolves at inbox acceptance: the child owns its own turns from there, so this call neither waits for nor collects a result, and the child does not report back — its transcript by that id is the source of its output, and the optional global `send_message` tool sends it more work. Starting continuable work does not require `send_message` to be loaded. See the [background subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md), the [continuable subagents Agent Note](../../../.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md), and the [merged-service Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md).
+With `run_in_background: true`, `backgroundMode` selects the route. `one-shot` registers a plain parent-owned Task and returns canonical `{ kind: 'background', taskId }`, rendered as `started background subagent task <id>`, even when the provider supports continuable children; generic task tools own its later status, collection, cancellation, and notices. `continuable` requires a provider with the `prepareContinuable` capability, calls `ctx.subagents.startContinuable()`, and returns `{ kind: 'continuable', subagentId }`, rendered as `started subagent <childId>`. The continuable route resolves at inbox acceptance: the child owns its own turns from there, so this call neither waits for nor collects a result. The child's transcript by that id remains the source of its detailed output, and the optional global `send_message` tool sends it more work. The parent is not left guessing when to look, though: the continuation service delivers one settlement notice to it whenever a continuable child's Activation ends, which is why the schema tells the model it will be told and must not poll. Starting continuable work does not require `send_message` to be loaded. See the [background subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md), the [continuable subagents Agent Note](../../../.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md), and the [merged-service Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md).
 
 `toolFilter` changes the child's global tool layer but is not a parent-derived authority ceiling. See the [agent-scope security non-goal](../../../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md#security-and-authority-are-non-goals).
 
@@ -37,7 +37,7 @@ Foreground and background calls are exclusive. Children may share the parent's w
 
 #### What the model sees
 
-The generated default [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent) under this instance's configured name while its provider exists. Provider context inheritance changes the tool and prompt descriptions; enabled background mode adds `run_in_background`, and continuable mode describes starting a background subagent that keeps its conversation and returns its subagent id, while one-shot mode describes a background task id collected with `task_output` and stopped with `task_kill`.
+The generated default [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent) under this instance's configured name while its provider exists. Provider context inheritance changes the tool and prompt descriptions; enabled background mode adds `run_in_background`, and continuable mode describes starting a background subagent that keeps its conversation, returns its subagent id, and reports its own completion — so the model is told never to poll or wait on it — while one-shot mode describes a background task id collected with `task_output` and stopped with `task_kill`.
 
 #### Token effect
 
@@ -65,11 +65,11 @@ Append-only; newly visible content follows the reusable request prefix and does
 
 #### What the model sees
 
-Start returns exactly `started subagent <childId>` in configured continuable mode, or `started background subagent task <id>` in configured one-shot mode. In one-shot mode the generic task surface provides later status, final output, cancellation responses, and notices. In continuable mode the child does not report back; an independently loaded `send_message` tool delivers follow-ups, and the child's transcript by its id is the source of its output.
+Start returns exactly `started subagent <childId>` in configured continuable mode, or `started background subagent task <id>` in configured one-shot mode. In one-shot mode the generic task surface provides later status, final output, cancellation responses, and notices. In continuable mode this tool returns no result of its own; the child's settlement reaches the parent as a [service-owned notice](../subagent/README.md#settlement-notice), an independently loaded `send_message` tool delivers follow-ups, and the child's transcript by its id is the source of its detailed output.
 
 #### Token effect
 
-The acknowledgement is retained; a one-shot final output enters parent history only when collected or injected, while a continuable child's output never returns through this tool.
+The acknowledgement is retained; a one-shot final output enters parent history only when collected or injected, while a continuable child's output never returns through this tool — its settlement notice arrives independently of any tool result.
 
 #### KV Cache effect
 
@@ -77,6 +77,6 @@ Append-only; newly visible content follows the reusable request prefix and does
 
 ## Known Limitations and Deferred Work
 
-- **Background runs expose no result through this tool** — a one-shot task's final output is collected through the generic task surface, and a continuable child's output stays in its own session, read by its subagent id.
+- **Background runs expose no result through this tool** — a one-shot task's final output is collected through the generic task surface, and a continuable child's output stays in its own session, read by its subagent id. The settlement notice states how that child ended and carries its closing message, but it is not this call's return value and cannot be awaited here.
 - **Duplicate names across waiting instances are detected late** (`TODO(subagent-dup-toolname)`) — preventing provider-registration rollback requires a registry of intended names.
 - **Child policy is fixed per instance** — another model, persona, tool filter, or depth cap requires another distinctly named tool.

packages/subagent/tool-subagent/README.zh.md

@@ -10,7 +10,7 @@
 
 前台调用会让执行信号贯穿启动和执行，等待 `run.result`，并且在返回前总会等待 `run.dispose()`。只有 `completed` 会返回规范值 `{ kind: 'foreground', runId, output: JsonValue[] }`，并渲染为相同的最终文本；中止、拒绝、token 上限和其他失败都会变成出错的工具结果，其消息在终止原因标题之后附带子代理保留下来的部分文本（即 `SubagentResult.output` 的选取结果）——被截断的回答不会被报告为成功，也绝不会被悄悄丢弃。如果结果收集与 dispose（资源释放）都 reject，出错的结果会保留两项诊断信息。
 
-设置 `run_in_background: true` 后，`backgroundMode` 会选择路由。`one-shot` 会注册一个归父级所有的普通 Task，并返回规范值 `{ kind: 'background', taskId }`，渲染为 `started background subagent task <id>`，即使提供方支持可继续子 agent 也不例外；通用 Task 工具负责其后续状态、收集、取消和通知。`continuable` 要求提供方具备 `prepareContinuable` 能力，调用 `ctx.subagents.startContinuable()`，并返回 `{ kind: 'continuable', subagentId }`，渲染为 `started subagent <childId>`。可继续路由在 inbox 接受时结算：子 agent 自此拥有自己的轮次，因此该调用既不等待也不收集结果，而且子 agent 不会回报——通过该 id 查看其 transcript（文本记录）即是其输出来源，可选的全局 `send_message` 工具则向其发送更多工作。启动可继续工作不要求加载 `send_message`。见 [后台 subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md)、[可继续的 subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md)和[服务合并 Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md)。
+设置 `run_in_background: true` 后，`backgroundMode` 会选择路由。`one-shot` 会注册一个归父级所有的普通 Task，并返回规范值 `{ kind: 'background', taskId }`，渲染为 `started background subagent task <id>`，即使提供方支持可继续子 agent 也不例外；通用 Task 工具负责其后续状态、收集、取消和通知。`continuable` 要求提供方具备 `prepareContinuable` 能力，调用 `ctx.subagents.startContinuable()`，并返回 `{ kind: 'continuable', subagentId }`，渲染为 `started subagent <childId>`。可继续路由在 inbox 接受时结算：子 agent 自此拥有自己的轮次，因此该调用既不等待也不收集结果。通过该 id 查看其 transcript（文本记录）仍是其详细输出的来源，可选的全局 `send_message` 工具则向其发送更多工作。不过父级无需猜测何时查看：每当可继续子 agent 的 Activation 结束，继续执行服务都会向父级投递一条结算通知——正因如此，schema 才告诉模型它会被通知，且不得轮询。启动可继续工作不要求加载 `send_message`。见 [后台 subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md)、[可继续的 subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md)和[服务合并 Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md)。
 
 `toolFilter` 会改变子 agent 的全局工具层，但不是从父级派生的权限上限。见 [agent 作用域的安全非目标](../../../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md#security-and-authority-are-non-goals)。
 
@@ -37,7 +37,7 @@
 
 #### 模型看到的内容
 
-当提供方存在时，以当前实例配置的名称公开已生成的默认 [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent)。提供方是否继承上下文会改变工具描述和提示词描述；启用后台模式会添加 `run_in_background`，可继续模式描述为启动一个保留其对话并返回子 agent id 的后台子 agent，而一次性模式描述为返回一个用 `task_output` 收集、用 `task_kill` 停止的后台任务 id。
+当提供方存在时，以当前实例配置的名称公开已生成的默认 [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent)。提供方是否继承上下文会改变工具描述和提示词描述；启用后台模式会添加 `run_in_background`，可继续模式描述为启动一个保留其对话、返回子 agent id 并会自行报告完成的后台子 agent——因此模型被告知绝不要轮询或等待它——而一次性模式描述为返回一个用 `task_output` 收集、用 `task_kill` 停止的后台任务 id。
 
 #### Token 影响
 
@@ -65,11 +65,11 @@
 
 #### 模型看到的内容
 
-在配置的可继续模式下，启动时返回内容恰为 `started subagent <childId>`；在配置的一次性模式下，则返回 `started background subagent task <id>`。一次性模式下，通用 Task 接口提供后续状态、最终输出、取消响应和通知。可继续模式下，子 agent 不会回报；独立加载的 `send_message` 工具会投递后续消息，而通过其 id 查看子 agent 的 transcript 即是其输出来源。
+在配置的可继续模式下，启动时返回内容恰为 `started subagent <childId>`；在配置的一次性模式下，则返回 `started background subagent task <id>`。一次性模式下，通用 Task 接口提供后续状态、最终输出、取消响应和通知。可继续模式下，本工具不返回自己的结果；子 agent 的结算会以[服务负责的通知](../subagent/README.md#settlement-notice)到达父级，独立加载的 `send_message` 工具会投递后续消息，而通过其 id 查看子 agent 的 transcript 即是其详细输出来源。
 
 #### Token 影响
 
-确认消息会被保留；一次性最终输出只在收集或注入时进入父级历史，而可继续子 agent 的输出绝不会通过本工具返回。
+确认消息会被保留；一次性最终输出只在收集或注入时进入父级历史，而可继续子 agent 的输出绝不会通过本工具返回——其结算通知独立于任何工具结果到达。
 
 #### KV Cache 影响
 
@@ -77,6 +77,6 @@
 
 ## 已知限制与暂缓事项
 
-- **后台运行不通过本工具公开结果**：一次性任务的最终输出通过通用 Task 接口收集，可继续子 agent 的输出留在其自身会话中，按其 subagent id 读取。
+- **后台运行不通过本工具公开结果**：一次性任务的最终输出通过通用 Task 接口收集，可继续子 agent 的输出留在其自身会话中，按其 subagent id 读取。结算通知会说明该子 agent 如何结束并携带其收尾消息，但它不是本次调用的返回值，也无法在此等待。
 - **等待中实例的重复名称发现较晚**（`TODO(subagent-dup-toolname)`）：若要阻止提供方注册回滚，需要一份预期名称注册表。
 - **每个实例的子 agent 策略固定**：其他模型、persona、工具过滤器或深度上限都需要另一个名称不同的工具。

packages/subagent/tool-subagent/src/index.ts

@@ -262,12 +262,13 @@ export function apply(ctx: Context, config: Config): void {
     disposeTool = ctx.tools.register(defineTool({
       name: config.toolName ?? 'subagent',
       description: wording.description + (backgroundEnabled
-        // The return channel is a separately installed capability this package
-        // cannot observe, so this describes only this call's result.
+        // The completion notice is the continuation service's own behavior, not
+        // a separately installed capability, so this promise holds whenever the
+        // continuable background path is reachable at all.
         ? continuable
           ? ' Set `run_in_background: true` to start a background subagent that keeps its conversation:'
-          + ' you receive only its subagent id, never its result, and it works on its own. Use this for'
-          + ' work whose result you do not need returned by this call; `send_message` sends it more work.'
+          + ' this call returns only its subagent id, and the subagent works on its own from there. You'
+          + ' are told when it finishes, so never poll or wait on it; `send_message` sends it more work.'
           : ' Set `run_in_background: true` to return a task id; collect with `task_output` and stop with `task_kill`.'
         : ''),
       parameters: {
@@ -286,7 +287,7 @@ export function apply(ctx: Context, config: Config): void {
             type: 'boolean' as const,
             description: continuable
               ? 'Run as a background subagent that keeps its conversation and return only its subagent id. '
-              + 'This call never returns its result; send it more work with send_message.'
+              + 'This call does not wait for it; you are told when it finishes. Send it more work with send_message.'
               : 'Run as a background task and return its id; collect with task_output or stop with task_kill.',
           },
         } : {},