fix(web): follow a blank session's preset switch in the slash catalog

Presets own the rows that decide what a session's `/` menu contains, but
both browser catalogs cache per session and had no invalidation edge for a
recompose: `commands/changed` is registry-wide and recomposing registers
nothing, so the menu kept serving the composition the session no longer ran.

The host stream now frames the logged `agent-preset/selected` commit as
`host/session-preset-changed`; the runtime bridges it to the typed
`session/preset-changed` event, `ui-command` soft-refreshes that session's
directory key and `ui-skill` invalidates its catalog entry.

Reaching the host on a second switch was a separate defect: the list-row
identity guard compared every summary field except `agentPreset`, and the
merge keeps the row's `updatedAt`, so a switched row looked unchanged and
served its cached instance forever. The hero chip compares the pick against
that row, so switching back to the creation-time preset sent no RPC at all.

packages/client/ui-skill/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/client/ui-skill/README.md
-README.md: 677ac215d299fca695a6b27c564779ef1d3fd6ee
-README.zh.md: 8f1f69b26a932aaa300bdda1d4ec7b2fa749fe3c
+README.md: f6bf71bab5c5335d3da073101bcbafb30d1c2757
+README.zh.md: eae61780df7ccee350956dc542ebda70c671feb3

packages/client/ui-skill/README.md

@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-Skill invocation source, browser half: registers the `/`-trigger `skill` source into `ctx.slash`. Ordinary-session candidates come from the `skill.list` RPC addressed by the per-call `ClientSessionContext` projection's `{sessionId}`, with the host resolving `cwd` from the session header. The host serves every user-invocable skill; a `modelInvocable: false` entry (a `disable-model-invocation` skill, whose only entry point is this path) wears the user-only marker as a description prefix in the active language. Catalog-addressed continuable children resolve no skill candidates locally because the existing skill RPC requires an attached session; viewing their persisted history must not activate them. Catalogs cache per ordinary session with a single-flight fetch; the scope-birth `warm` hook prewarms the session's entry and `connection/reset` clears everything. Results filter by `startsWith(query)`.
+Skill invocation source, browser half: registers the `/`-trigger `skill` source into `ctx.slash`. Ordinary-session candidates come from the `skill.list` RPC addressed by the per-call `ClientSessionContext` projection's `{sessionId}`, with the host resolving `cwd` from the session header. The host serves every user-invocable skill; a `modelInvocable: false` entry (a `disable-model-invocation` skill, whose only entry point is this path) wears the user-only marker as a description prefix in the active language. Catalog-addressed continuable children resolve no skill candidates locally because the existing skill RPC requires an attached session; viewing their persisted history must not activate them. Catalogs cache per ordinary session with a single-flight fetch; the scope-birth `warm` hook prewarms the session's entry, `session/preset-changed` drops that one session's entry (the catalog belongs to the preset, and a blank session may switch after the warm), and `connection/reset` clears everything. Results filter by `startsWith(query)`.
 
 A pick lands the literal `/name ` text and the prompt ships the same literal ([slash-pipeline Agent Note](../../../.agents/notes/implemented/architecture/2026-07-25-web-input-machine-and-slash-pipeline.md)) — this source implements no adjudication hooks and no reference codec. Determinism lives host-side: the pre-step gesture boundary (`dsh-tool-skill`) recognizes whitespace-bounded `/name` tokens naming user-invocable skills anywhere in a user message and injects the rendered `<skill_content>` for every front end, so a menu pick, a hand-typed token, and a TUI/ACP prompt all load the skill the same way. A name shared with a host command still resolves to the command: adjudication claims the line client-side before it ever becomes a prompt — deliberate precedence, matching peer products. The list RPC rides the plugin's root-context connection captured at registration — the source never reads services off a per-call argument; draft chip visuals derive from the `lexicon` scan.
 

packages/client/ui-skill/README.zh.md

@@ -2,7 +2,7 @@
 
 [English](README.md) | 中文
 
-skill（技能）调用 source 的浏览器端：把 `/` 触发的 `skill` source 注册进 `ctx.slash`。普通会话的候选来自 `skill.list` RPC，以每次调用的 `ClientSessionContext` 投影中的 `{sessionId}` 寻址，host 从会话 header 解析 `cwd`。宿主提供每一个用户可调用的 skill；`modelInvocable: false` 的条目（即 `disable-model-invocation` skill，此路径是其唯一入口）会以当前语言把仅限用户标记作为描述前缀带上。由目录寻址的可继续 subagent 在客户端解析为没有 skill 候选，因为现有 skill RPC 要求会话已挂载；查看其持久化历史不得激活它。目录按普通会话缓存，拉取走 single-flight；scope 创建时的 `warm` 钩子预热该会话的缓存项，`connection/reset` 清空全部缓存。结果按 `startsWith(query)` 过滤。
+skill（技能）调用 source 的浏览器端：把 `/` 触发的 `skill` source 注册进 `ctx.slash`。普通会话的候选来自 `skill.list` RPC，以每次调用的 `ClientSessionContext` 投影中的 `{sessionId}` 寻址，host 从会话 header 解析 `cwd`。宿主提供每一个用户可调用的 skill；`modelInvocable: false` 的条目（即 `disable-model-invocation` skill，此路径是其唯一入口）会以当前语言把仅限用户标记作为描述前缀带上。由目录寻址的可继续 subagent 在客户端解析为没有 skill 候选，因为现有 skill RPC 要求会话已挂载；查看其持久化历史不得激活它。目录按普通会话缓存，拉取走 single-flight；scope 创建时的 `warm` 钩子预热该会话的缓存项，`session/preset-changed` 丢弃该会话这一项（目录属于 preset，而空会话可能在预热之后才切换），`connection/reset` 清空全部缓存。结果按 `startsWith(query)` 过滤。
 
 pick 会落下字面文本 `/name `，提示词发出的就是同一段字面文本（[slash 流水线 Agent Note](../../../.agents/notes/implemented/architecture/2026-07-25-web-input-machine-and-slash-pipeline.md)）——本 source 不实现任何裁决钩子，也没有引用 codec。确定性在宿主侧：pre-step 手势边界（`dsh-tool-skill`）识别用户消息中任意位置、以空白为界、指名用户可调用 skill 的 `/name` token，并为每一种前端注入渲染后的 `<skill_content>`，因此菜单 pick、手动键入的 token 与 TUI/ACP（Agent Client Protocol）提示词都以同一种方式加载 skill。与宿主命令同名的名称仍解析为命令：裁决在客户端把该行认领走，它根本不会成为提示词——这是有意的优先级，与同行产品一致。列表 RPC 使用插件注册时捕获的根上下文连接——source 绝不从每次调用的参数上读取服务；草稿 chip 视觉由 `lexicon` 扫描派生。
 

packages/client/ui-skill/src/client/index.ts

@@ -17,7 +17,9 @@
  * Catalog fetches are cached per session (the small twin of the ui-command
  * directory): the per-keystroke candidates re-poll filters a settled
  * snapshot locally, so one session costs one RPC. The scope-birth warm hook
- * prewarms the session's key; connection/reset clears everything — the host
+ * prewarms the session's key; a preset switch drops that one key (the
+ * catalog is the preset's, and a blank session may switch after the warm);
+ * connection/reset clears everything — the host
  * catalog may differ across generations. A shared in-flight fetch
  * deliberately outlives any single menu interaction: closing the menu must
  * not kill the prewarm other consumers will hit, so it carries its own
@@ -174,6 +176,9 @@ export function apply(ctx: ClientContext): void {
     },
   }
   const slash = ctx.get('slash') as SlashServiceContract
+  // A preset decides which skill providers an agent reads, so a switched
+  // session's cached catalog belongs to the composition it no longer runs.
+  ctx.on('session/preset-changed', invalidate)
   ctx.on('connection/reset', clearAll)
   ctx.effect(() => {
     const unregister = slash.registerSource(source)

packages/client/ui-skill/tests/browser-plugin.spec.ts

@@ -263,6 +263,21 @@ describe('catalog cache', () => {
     expect(payloads).toHaveLength(2)
   })
 
+  it('session/preset-changed clears only the recomposed session', async () => {
+    const { list, payloads } = countingList()
+    const { ctx, source } = await bench(list)
+    await source.candidates(proj('s1'), req(''))
+    await source.candidates(proj('s2'), req(''))
+    expect(payloads).toHaveLength(2)
+    // The catalog a preset supplies is the preset's; the other session's
+    // composition did not change, so its cached catalog still holds.
+    ctx.emit('session/preset-changed', sid('s1'), 'minimal')
+    await source.candidates(proj('s1'), req(''))
+    await source.candidates(proj('s2'), req(''))
+    expect(payloads).toHaveLength(3)
+    expect(payloads[2]).toEqual({ sessionId: 's1' })
+  })
+
   it('connection/reset clears every cached session', async () => {
     const { list, payloads } = countingList()
     const { ctx, source } = await bench(list)