fix(subagent): compose children from their parent's preset

Tool and prompt-section visibility is inherited along dsh-scope's parent
chain, and an agent's scope key is minted with no parent. Per-session agent
presets moved every model-facing row onto the agent plane and made
AgentPresets.mount() the one thing that binds that link, from the api-proxy's
session create, resume, and fork paths. The two in-process subagent drivers
installed only the per-child persona and tool filter, so a child's scope chain
had length one and its registry view resolved the global layer alone — which
is empty wherever a preset roster is composed. One-shot children reached the
model with no tools, continuable ones with only the host-plane `report`, and
neither carried its parent's persona, workspace context, or skill catalog.

AgentPresets.composeFrom() joins one agent to the standing composition another
already runs on. It is a bind, not a mount: the child gets its parent's exact
generation, so a composition edited since the parent started cannot fork it
onto another one, and it is synchronous, which is what lets a child creation
window use it. applyChildComposition() now takes the parent and performs the
join first, making a child composed without it unrepresentable at the call
sites. childSessionMeta() records the joined id so a cold read rebuilds the
composition the child actually ran under.

The audit that followed found two api-proxy readers on the wrong authority:
presenterScopeFor() and the live-agent branch of assertPresetUnchanged() both
read header.agentPreset, which goes stale the moment a blank session switches
preset. A switched session's cold transcript resolved presenters in the older
composition's layer and silently degraded to generic cards, and the gateway
refused to adopt a live session under the preset it actually runs while
accepting the one it left. Both now resolve through resolveSessionPreset(),
matching the resume branch fifteen lines above. The owning architecture Agent
Note carried the stale claim that the header records what a session runs; it
is corrected to name the header/log pair and its three readers.

Fixes #2165

.agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.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 .agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.md
-2026-08-03-per-session-agent-presets.md: 6f1643c25008c3363cb10adb7fbff7afeea31cbe
-2026-08-03-per-session-agent-presets.zh.md: 7afe9ade5c98fadb96384a7e0acd47531c370e0c
+2026-08-03-per-session-agent-presets.md: c39117ab0de001650a95f98ccf3e42f3a5034c92
+2026-08-03-per-session-agent-presets.zh.md: 5e98a2865013a355c134317ded8a4f2ddaccf42c

.agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.md

@@ -31,7 +31,7 @@ Which preset an unnamed session gets is a user setting (`agent-presets.default`)
 
 ## Consequences
 
-**The effective default is read per resolution, never snapshotted.** A cached value would need a `watch` subscription and a reload path to stay honest, and the resolved scope already re-reads a hot-reloaded document. Reading through is also what makes the boundary correct rather than merely cheap: the new value applies to the next session created, and every running session keeps the composition it was built from. That invariant is the same one the session header enforces from the other side — the header records the id a session actually runs, so a resume rebuilds that composition rather than today's default, and the gateway rejects an attempt to adopt a live session under a different one. A snapshot would make the two disagree at exactly the moment the setting changes.
+**The effective default is read per resolution, never snapshotted.** A cached value would need a `watch` subscription and a reload path to stay honest, and the resolved scope already re-reads a hot-reloaded document. Reading through is also what makes the boundary correct rather than merely cheap: the new value applies to the next session created, and every running session keeps the composition it was built from. That invariant is the same one the session log enforces from the other side — the header records the id a session was CREATED with and an `agent-preset/selected` event records any later blank-session switch, so a reader resolves the pair (`resolveSessionPreset`) and never the header alone: a resume rebuilds the composition its history was produced under rather than today's default, a cold transcript's presenters resolve in that composition's layer, and the gateway rejects an attempt to adopt a live session under a preset other than the one it currently runs. A snapshot would make the two disagree at exactly the moment the setting changes.
 
 **A directly-plugged subtree is invisible to the boot audit.** It never links itself to an `Entry`, so it is absent from `ctx.loader.entries()` and `assertEntriesActivated` cannot see it. The mount audits its own rows instead, reading the tree through an `Include` subclass that publishes it.
 

.agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.zh.md

@@ -31,7 +31,7 @@ Status: implemented
 
 ## 后果
 
-**有效默认值在每次解析时读取，从不快照。** 缓存下来就需要一个 `watch` 订阅和一条重载路径才能保持诚实，而解析后的 scope 本来就会重读热重载过的文档。读穿也不只是省事，它让边界本身是对的：新值作用于**下一个新建的会话**，每个运行中的会话保持它被构建时的那份组装。这条不变量正是 session header 从另一侧执行的同一条——header 记录会话实际运行的 id，因此恢复重建的是那份组装而不是当下的默认值，网关也会拒绝把一个活着的会话收编到另一个 preset 之下。快照会让两者恰好在设置改变的那一刻各说各话。
+**有效默认值在每次解析时读取，从不快照。** 缓存下来就需要一个 `watch` 订阅和一条重载路径才能保持诚实，而解析后的 scope 本来就会重读热重载过的文档。读穿也不只是省事，它让边界本身是对的：新值作用于**下一个新建的会话**，每个运行中的会话保持它被构建时的那份组装。这条不变量正是 session 日志从另一侧执行的同一条——header 记录会话**创建时**的 id，此后空白期的任何切换由 `agent-preset/selected` 事件记录，因此读取方解析的是两者之和（`resolveSessionPreset`）、绝不单看 header：恢复重建的是其历史所产出的那份组装而不是当下的默认值，冷读记录的 presenter 在那份组装的层里解析，网关也会拒绝把一个活着的会话收编到它当前运行的 preset 以外的 preset 之下。快照会让两者恰好在设置改变的那一刻各说各话。
 
 
 **直接挂载的子树对启动审计不可见。** 它不会把自己关联到 `Entry`，因此不在 `ctx.loader.entries()` 中，`assertEntriesActivated` 也看不到它。改由挂载过程自行校验各行，通过一个会公开自身 tree 的 `Include` 子类读取。

.agents/notes/implemented/bug-fix/2026-08-10-child-agents-join-their-parent-preset.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/bug-fix/2026-08-10-child-agents-join-their-parent-preset.md
+2026-08-10-child-agents-join-their-parent-preset.md: c9917c48d10c2b2515284405ea52aed8b476f8b1
+2026-08-10-child-agents-join-their-parent-preset.zh.md: 09e4de5292b65e50bb3973704fd803c819be9f1c

.agents/notes/implemented/bug-fix/2026-08-10-child-agents-join-their-parent-preset.md

@@ -0,0 +1,47 @@
+# Agent Note: Child agents join their parent's preset composition
+
+Status: implemented
+
+English | [中文](2026-08-10-child-agents-join-their-parent-preset.zh.md)
+
+## Problem
+
+Tool and prompt-section visibility is inherited along `dsh-scope`'s parent chain, and an agent's scope key is minted with no parent. [Per-session agent presets](../architecture/2026-08-03-per-session-agent-presets.md) moved every model-facing row onto the agent plane and made `AgentPresets.mount()` the one thing that binds that parent link — from the api-proxy's session create, resume, and fork paths. The two in-process subagent drivers compose their children through `applyChildComposition()`, which installed only the per-child persona and tool filter, so a child's scope chain had length one and its registry view resolved the global layer alone.
+
+That layer is now empty in any deployment with a preset roster: the web-app patch layer disables every host-plane tool row. A one-shot child therefore reached the model with zero tools, a continuable child with only the host-plane `report`, and neither carried its parent's persona, workspace context, plan-mode section, or skill catalog. The fork path had already been given the same treatment for the same reason; delegation had not.
+
+The child's durable header compounded it. `childSessionMeta()` recorded no preset, so a cold read of a child session resolved the deployment default — a tool set the child never ran under, which is exactly what the model-visible ⟺ logged rule exists to prevent.
+
+## Decision
+
+`AgentPresets.composeFrom(agentCtx, parentCtx)` joins one agent to the standing composition another already runs on, and returns the preset id joined. It locates the parent's mount through `standingMountFor()` — the agent's key is parented to its preset's standing key, the same relation `serviceForAgent()` reads — and binds the child's key to that same standing key, keeping the binding under the roster's sole re-link authority. A parent that joined no preset yields no join and no error, which is the rosterless deployment: its model-facing rows sit in the host composition, where the child already resolves them through the global layer.
+
+This is a bind, not a mount, and both differences are load-bearing. The child gets its parent's exact generation, so a composition file edited since the parent started cannot hand the child a different one than its parent's history was produced under, and a preset deleted since cannot fail a child whose parent keeps running. It is also synchronous, which is what lets the child creation windows use it — both in-process drivers compose inside a synchronous `setup`.
+
+`applyChildComposition(childCtx, parent, composition)` takes the parent and performs the join before applying the child's own registrations. The parameter is the point: it makes composing a child without the join unrepresentable at the call sites, rather than leaving each new driver to remember a second step. `childSessionMeta()` records the joined id through `AgentPresets.composedPreset()`, read from the parent's live scope chain rather than its header, because a parent that switched preset while blank runs on the newer composition while its header still names the older one.
+
+`dsh-subagent` reaches the roster through `ctx.get('agentPresets')` with a type-only import and an optional peer dependency — the documented opportunistic-consumption pattern it already uses for `sandboxPolicy` and `approval`.
+
+## Alternatives considered
+
+**Re-mount the parent's preset by id in the child's setup.** Rejected on both semantics and mechanics. It re-reads the roster and re-stats the composition file, so an edit since the parent started forks the child onto a different generation, and a preset deleted since fails the child while its parent runs on. `mount()` is also asynchronous, which the synchronous creation windows cannot accept without restructuring both drivers.
+
+**Bind the child's key to the PARENT's key rather than to the standing mount.** Rejected because it changes what a child inherits: the parent's own scope layer carries its per-agent restrictions, which would then intersect into every descendant, and a child outliving its parent would hang off a disposed agent's key. Joining the standing mount gives the child its parent's composition and nothing else.
+
+**Extend the continuable activation setup registry to cover one-shot children.** Rejected because that registry's contribution type is synchronous `(childCtx) => () => void` with per-installation revocation, modelling deployment capabilities that come and go, while a preset join is a one-time bind with no revocation of its own. Widening it would have made the omission possible again for any driver that skipped the registry.
+
+**Let `dsh-subagent` import `resolveSessionPreset` and mount by the resolved id.** Rejected because it makes the preset roster a hard module edge for a package that must work without one, and it lands back on the remount semantics above.
+
+**Leave the durable header alone and fix only the live join.** Rejected because the live child and the same child read cold would then disagree about which composition produced its history — the same class of defect, moved rather than fixed.
+
+## Testing
+
+`packages/preset/agent-presets/tests/mount.spec.ts` covers the join against real fixture compositions: the child sees its parent's tools and prompt sections, no second generation is mounted, the join survives the parent's disposal (a background child outliving its parent), the reported id matches, a parent without a preset joins nothing, and an unscoped context is refused.
+
+`packages/subagent/subagent-inprocess/tests/preset-inheritance.spec.ts` asserts the model-visible result through `startInProcessRun()` on a host composition carrying no model-facing rows: the schemas in the child's own request, its parent's prompt section, the recorded header preset, and a parent that switched preset while blank.
+
+## Consequences
+
+Delegation now costs a scope-parent bind per child and nothing else — no extra plugin instances, no roster read, no failure mode. A child's capabilities are exactly its parent's, minus whatever its own `toolFilter` removes; a per-subagent preset ("agent types") remains unbuilt and would be a new request field rather than a change to this join.
+
+`applyChildComposition()` changed shape, so any future out-of-tree in-process driver must supply the parent. That is the intended cost: the previous signature let a caller compose a capability-less child and get no error.

.agents/notes/implemented/bug-fix/2026-08-10-child-agents-join-their-parent-preset.zh.md

@@ -0,0 +1,47 @@
+# Agent Note: Child agents join their parent's preset composition
+
+Status: implemented
+
+[English](2026-08-10-child-agents-join-their-parent-preset.md) | 中文
+
+## Problem
+
+工具与提示段的可见性沿 `dsh-scope` 的父链继承，而 agent 的 scope key 铸造出来时没有父。[逐会话 agent preset](../architecture/2026-08-03-per-session-agent-presets.md) 把所有面向模型的行搬到了 agent 平面，并让 `AgentPresets.mount()` 成为绑定那条父链的唯一途径——调用点在 api-proxy 的会话创建、恢复与 fork 路径上。两个进程内 subagent 驱动通过 `applyChildComposition()` 组装子 agent，而它只安装了逐子 agent 的 persona 与工具限制，于是子 agent 的 scope 链长度为一，其注册表视图只能解析到全局层。
+
+在任何配置了 preset roster 的部署里，那一层现在是空的：web-app 补丁层禁用了全部宿主平面工具行。因此一次性子 agent 抵达模型时工具为零，可继续子 agent 只剩宿主平面的 `report`，两者都不带父方的 persona、工作区上下文、plan-mode 段与技能目录。fork 路径此前已因同一理由做过相同处理；委派没有。
+
+子 agent 的持久化 header 让问题更进一步。`childSessionMeta()` 不记录任何 preset，于是冷读一个子会话解析到的是部署默认值——一套该子 agent 从未运行过的工具集，而这正是"模型可见 ⟺ 已记录"规则要杜绝的情形。
+
+## Decision
+
+`AgentPresets.composeFrom(agentCtx, parentCtx)` 让一个 agent 加入另一个 agent 已在运行的常驻组装，并返回所加入的 preset id。它通过 `standingMountFor()` 定位父方的挂载——agent 的 key 认父到其 preset 的常驻 key，正是 `serviceForAgent()` 读取的同一关系——再把子 agent 的 key 绑到同一个常驻 key 上，绑定句柄仍归 roster 独有的重链权威持有。未加入任何 preset 的父方不产生加入、也不报错，那就是无 roster 的部署：它面向模型的行位于宿主组装中，子 agent 已经能通过全局层解析到它们。
+
+这是认父而非挂载，两处差别都要紧。子 agent 拿到的是父方那个确切的代际，因此父方启动后被编辑过的组装文件不可能把与父方历史所产出时不同的另一个代际交给它，此后被删除的 preset 也不可能让一个父方仍在运行的子 agent 失败。它还是同步的，这正是子 agent 创建窗口能够使用它的前提——两个进程内驱动都在同步的 `setup` 中完成组装。
+
+`applyChildComposition(childCtx, parent, composition)` 接收父方，并在应用子 agent 自身注册之前完成加入。这个参数正是要点所在：它让"组装子 agent 却不做该加入"在各调用点无法表达，而不是把第二个步骤留给每个新驱动去记住。`childSessionMeta()` 通过 `AgentPresets.composedPreset()` 记录所加入的 id，该值从父方**活着的** scope 链读取而不是从其 header 读取，因为在空白期切换过 preset 的父方运行在更新的那份组装上，而它的 header 仍写着旧的那个。
+
+`dsh-subagent` 以类型级导入加可选 peer 依赖的方式，通过 `ctx.get('agentPresets')` 触达 roster——这正是它对 `sandboxPolicy` 与 `approval` 已在使用的、有明确文档的机会性消费模式。
+
+## Alternatives considered
+
+**在子 agent 的 setup 里按 id 重新挂载父方的 preset。** 语义与机制两方面都不成立而被否决。它会重读 roster 并重新 stat 组装文件，因此父方启动后的一次编辑就会把子 agent 分叉到另一个代际，而此后被删除的 preset 会让子 agent 失败、父方却照常运行。`mount()` 还是异步的，同步的创建窗口无法在不重构两个驱动的前提下接受它。
+
+**把子 agent 的 key 绑到**父方的** key 而不是常驻挂载上。** 否决，因为这改变了子 agent 继承的内容：父方自己的 scope 层携带其逐 agent 限制，那些限制会就此与每个后代求交，而活得比父方久的子 agent 会挂在一个已 dispose 的 agent key 上。加入常驻挂载给到子 agent 的是父方的组装，仅此而已。
+
+**扩展可继续 activation setup 注册表以覆盖一次性子 agent。** 否决，因为该注册表的贡献类型是同步的 `(childCtx) => () => void` 并带有逐次安装的撤销，建模的是会来会走的部署能力，而 preset 加入是一次性认父、自身没有撤销可言。扩展它反而会让任何绕过该注册表的驱动重新具备遗漏的可能。
+
+**让 `dsh-subagent` 导入 `resolveSessionPreset` 并按解析出的 id 挂载。** 否决，因为这会给一个必须在没有 roster 时也能工作的包引入硬模块边，而且最终仍落回上述的重新挂载语义。
+
+**只修活着的加入，不动持久化 header。** 否决，因为那样活着的子 agent 与冷读同一个子 agent 会对"哪份组装产出了这段历史"给出不同答案——同一类缺陷，只是被搬了个地方而不是被修掉。
+
+## Testing
+
+`packages/preset/agent-presets/tests/mount.spec.ts` 用真实 fixture 组装覆盖该加入：子 agent 看到父方的工具与提示段、不会挂载出第二个代际、加入在父方 dispose 后依然成立（活得比父方久的后台子 agent）、上报的 id 一致、没有 preset 的父方不产生加入、以及无 scope 的上下文被拒绝。
+
+`packages/subagent/subagent-inprocess/tests/preset-inheritance.spec.ts` 在一个不含任何面向模型行的宿主组装上，通过 `startInProcessRun()` 断言模型可见的结果：子 agent 自身请求中的 schema、父方的提示段、记录下来的 header preset，以及在空白期切换过 preset 的父方。
+
+## Consequences
+
+委派现在的成本是每个子 agent 一次 scope 认父，再无其他——没有额外的插件实例、没有 roster 读取、没有新的失败模式。子 agent 的能力恰好等于父方的能力，减去它自己的 `toolFilter` 所移除的部分；逐 subagent 的 preset（"agent 类型"）仍未构建，那会是一个新的请求字段，而不是对这次加入的改动。
+
+`applyChildComposition()` 的形态变了，因此将来任何仓库外的进程内驱动都必须提供父方。这是刻意付出的代价：此前的签名允许调用方组装出一个毫无能力的子 agent 而不报任何错。