feat(ui): make a session that cannot send refuse to accept one

A default naming a route the Models page has since removed left the
composer saying 选择模型 while the input still accepted a message, which
then failed inside the adapter mid-turn.

`session.prompt` now refuses with `model-unavailable` before opening a
turn. That is the enforcement boundary: the method stays callable no
matter what a client disables. `session.models` reports the same fact as
`routable`, and ui-model pushes a block through the new
`ctx.conversation.blocks` registry so the bar renders the disabled
textarea it already renders without a workspace, carrying the blocker's
own reason. The push direction is forced — ui-model already depends on
ui-conversation, so ui-conversation cannot read it back.

The gate is `routable`, not "matches no advertised group": catalog
membership is advisory, so a route serving a model it stopped advertising
is missing from the groups yet perfectly usable, and `null` before the
first load never blocks so a slow Host cannot lock a working composer.

The scaffold gains a route-only adapter for fixture-less keyless
scenarios. Registering zero providers is a test artifact — every product
composition mounts one — and the goldens that froze the seat's fallback
label now show the model those scenarios actually route to.

packages/client/ui-model/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-model/README.md
-README.md: 5f9fc65939eb747d916fa5609423d3186d1fefde
-README.zh.md: 3ed8db3095d96e48813cf5b15a206ebf4c894950
+README.md: 5a6f998476629566d35af32efa5d8bc5072a872b
+README.zh.md: 2bb22c55f1ae5af59f21e254804329d288806a90

packages/client/ui-model/README.md

@@ -6,6 +6,8 @@ Model selection plugin, browser half: TWO entries over ONE per-session directory
 
 The Host-reported provider/model/reasoning target is the single selection fact, but it is echoed only when the exact route remains in the advertised groups; removing that catalog row leaves the routable target intact while the trigger prompts `Select model`, no stale row is synthesized, and no Effort row is shown until the user picks an advertised model. Directory loads and selections share a generation counter so an older response never overwrites a newer one; a connection reset drops every resident projection and repulls the Host-restored target before display. Provider-local metadata failures list inline while usable groups stay selectable, and selection failures retain the prior target and directory.
 
+When the Host reports that no adapter serves the session's route (`session.models.routable`), this plugin raises a composer block through `ctx.conversation.blocks` and the input goes inert with this plugin's own copy; recovering clears it without a reload. It follows `routable` and nothing else: a `null` — before the first load, or after one failed — never blocks, or a slow Host would lock a working composer, and catalog membership never blocks either, because a route serving a model it stopped advertising is missing from the groups yet perfectly usable. The trigger's own `Select model` fallback still covers that case, which is display, not a gate.
+
 Directories are per-session, resolved lazily through `ctx.models.directoryFor(sessionId)`, and disposed with the session scope. Addressed subagent sessions expose neither entry, and their directory rejects loads, selections, and reconnect refreshes, because ordinary Agent-bound model RPCs would activate persisted child history outside the direct-parent continuation seam.
 
 The `/client` export surface is the plugin body (`apply`/`inject`), `ModelService`, `ModelDirectory` with its state shape, and the seat's injected face type.

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

@@ -6,6 +6,8 @@
 
 Host 报告的提供方／模型／推理（reasoning）目标是唯一的选择事实，但只有当该精确路由仍在已公布分组中时才会回显；删除该目录行会保留仍可路由的目标，但触发器会提示 `Select model`，系统不会合成陈旧行，且在用户选择已公布的模型之前不会显示 Effort 行。目录加载与选择共享一个代次计数器，旧响应不会覆盖新结果；连接重置会丢弃所有常驻目录投影，并在显示前重新拉取 Host 恢复的目标。各提供方的元数据获取失败会内联列出，同时可用分组仍可选择；选择失败会保留先前的目标和目录。
 
+当宿主报告没有适配器服务该会话的路由（`session.models.routable`）时，本插件经 `ctx.conversation.blocks` 抬起一个编辑器 block，输入框随之变为惰性并显示本插件自己的文案；恢复后无需重新加载即自动清除。它只跟随 `routable`：`null`（首次加载之前，或加载失败之后）绝不阻断，否则一个慢的宿主就会锁死一个本来能用的编辑器；目录成员关系同样不阻断，因为一条仍在服务、只是不再公布该模型的路由不在分组里，却完全可用。触发器自己的 `Select model` 回退仍然覆盖那种情形——那是显示，不是闸门。
+
 目录按会话惰性解析（`ctx.models.directoryFor(sessionId)`），随会话作用域一并释放。已寻址 subagent 会话不公开任一入口，其目录会拒绝加载、选择与重新连接刷新，因为绑定到 agent（智能体）的普通模型 RPC 会在直接 parent 继续执行 seam 之外激活持久化 child 历史。
 
 `/client` 导出面为插件本体（`apply`/`inject`）、`ModelService`、`ModelDirectory` 及其状态形状、slot 注入面类型。

packages/client/ui-model/src/client/directory.ts

@@ -15,6 +15,14 @@ import { createSnapshotStore } from '@deepseek-ai/dsh-client-runtime/client'
 export interface ModelDirectoryState {
   /** Target the host reports for the next assembled step; null before the first load. */
   current: ModelTarget | null
+  /**
+   * Whether an adapter serves the current target's route, as the host reports
+   * it — null before the first load, which is NOT the same as blocked. Read
+   * this rather than "current matches no group": catalog membership is
+   * advisory, so a route serving a model it stopped advertising is missing
+   * from the groups yet perfectly usable.
+   */
+  routable: boolean | null
   /** Successfully loaded provider groups (last good load). */
   groups: readonly ModelProviderGroup[]
   /** Provider-local failures from the last load; usable groups stay usable. */
@@ -29,7 +37,7 @@ export interface ModelDirectoryState {
 export class ModelDirectory {
   /** The shared snapshot both entries render from (uSES-safe store). */
   readonly store: SnapshotStore<ModelDirectoryState> = createSnapshotStore<ModelDirectoryState>({
-    current: null, groups: [], failures: [], status: 'idle', error: null,
+    current: null, routable: null, groups: [], failures: [], status: 'idle', error: null,
   })
 
   /** Latest operation wins; an older response never overwrites a newer one. */
@@ -65,9 +73,10 @@ export class ModelDirectory {
       this.store.update((s) => { s.status = 'error'; s.error = `${result.error.code}: ${result.error.message}` })
       throw new Error(`session.models failed: ${result.error.code}: ${result.error.message}`)
     }
-    const { current, groups, failures } = result.value
+    const { current, routable, groups, failures } = result.value
     this.store.update((s) => {
       s.current = current
+      s.routable = routable
       s.groups = groups
       s.failures = failures
       s.status = 'ready'
@@ -102,7 +111,14 @@ export class ModelDirectory {
       this.store.update((s) => { s.status = 'error'; s.error = `${result.error.code}: ${result.error.message}` })
       throw new Error(`session.selectModel failed: ${result.error.code}: ${result.error.message}`)
     }
-    this.store.update((s) => { s.current = result.value.selected; s.status = 'ready'; s.error = null })
+    // The Host validated the route before accepting it, so a selection that
+    // landed is by construction one it can serve.
+    this.store.update((s) => {
+      s.current = result.value.selected
+      s.routable = true
+      s.status = 'ready'
+      s.error = null
+    })
   }
 
   /**
@@ -115,6 +131,7 @@ export class ModelDirectory {
     ++this.generation
     this.store.update((s) => {
       s.current = null
+      s.routable = null
       s.groups = []
       s.failures = []
       s.status = 'idle'

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

@@ -105,14 +105,16 @@ export const inject = ['command', 'connection', 'locale', 'sessions', 'slots']
  * @param ctx - client root context.
  */
 export function apply(ctx: ClientContext): void {
-  ctx.plugin(ModelService)
-
   ctx.effect(() => ctx.locale.register(NS, { zh, en }), 'ui-model: dictionaries')
 
   // Non-slot faces (the command description, the popup option builder) read
   // through the bound translate; the seat component reads the standard seat.
   const t = ctx.locale.bind(NS)
 
+  // The composer-block reason is this plugin's own copy, read at raise time so
+  // a locale change reaches the next publish.
+  ctx.plugin(ModelService, { blockReason: () => t('blocked.composer') })
+
   // Entry 1: the /model popupSelect over the shared directory. The command
   // description is registry-held text: it reads t() once at registration and
   // refreshes only on re-registration, not on locale change.

packages/client/ui-model/src/client/locales.ts

@@ -25,6 +25,7 @@ export const zh = {
   'action.reload': '重新加载',
   'warning.groupLoad': '{name} 加载失败：{message}',
   'empty.models': '没有可用的模型。',
+  'blocked.composer': '当前模型不可用，请先选择模型',
   'empty.efforts': '当前模型未提供推理等级。',
 } satisfies Record<string, string>
 
@@ -48,5 +49,6 @@ export const en = {
   'action.reload': 'Reload',
   'warning.groupLoad': '{name} failed to load: {message}',
   'empty.models': 'No models available.',
+  'blocked.composer': 'This model is unavailable — select one to continue',
   'empty.efforts': 'This model provides no reasoning effort levels.',
 } satisfies Record<ModelKey, string>

packages/client/ui-model/src/client/service.ts

@@ -36,11 +36,16 @@ export class ModelService extends Service {
 
   private readonly live: LiveState = { directories: new Map() }
 
+  /** Localized composer-block copy; this plugin owns the string it raises. */
+  private readonly blockReason: () => string
+
   /**
    * @param ctx - owning root context (the service registers itself as `models`).
+   * @param config - the bound translator for this plugin's own dictionary.
    */
-  constructor(ctx: Context) {
+  constructor(ctx: Context, config: { blockReason: () => string }) {
     super(ctx, 'models')
+    this.blockReason = config.blockReason
     ctx.on('connection/reset', () => {
       for (const directory of this.live.directories.values()) directory.resetConnected()
     })
@@ -74,6 +79,27 @@ export class ModelService extends Service {
       () => sessions.subagentAddress(sessionId) === undefined,
     )
     live.directories.set(sessionId, directory)
+    // The composer cannot read this plugin (the dependency runs one way), so
+    // the block is pushed: the Host says whether an adapter serves the
+    // session's route, and only a definite `false` makes the input inert.
+    // `null` — before the first load, or after one failed — must not, or a
+    // slow or unreachable Host would lock a working composer.
+    const conversation = this.ctx.get('conversation')
+    if (conversation !== undefined) {
+      const publish = (): void => {
+        conversation.blocks.set(sessionId, directory.store.getSnapshot().routable === false
+          ? { reason: this.blockReason() }
+          : undefined)
+      }
+      publish()
+      actx.effect(() => {
+        const stop = directory.store.subscribe(publish)
+        return () => {
+          stop()
+          conversation.blocks.set(sessionId, undefined)
+        }
+      }, 'ui-model: composer block')
+    }
     actx.effect(() => () => {
       directory.dispose()
       live.directories.delete(sessionId)

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

@@ -17,6 +17,7 @@ import type { ModelTarget } from '@deepseek-ai/dsh-client-connection/client'
 import type { CommandContribution, SelectOption } from '@deepseek-ai/dsh-client-ui-command/client'
 import type { ModelSelectInjected } from '../src/client/slots.ts'
 import { apply, inject } from '../src/client/index.ts'
+import { zh } from '../src/client/locales.ts'
 
 const sid = (k: string): SessionId => k as SessionId
 
@@ -59,7 +60,9 @@ async function bench() {
   ctx.provide('connection', { api: { sessions: {
     models: () => {
       calls.models += 1
-      return Promise.resolve({ result: { ok: true as const, value: { current, groups: GROUPS, failures: [] } } })
+      return Promise.resolve({
+        result: { ok: true as const, value: { current, routable, groups: GROUPS, failures: [] } },
+      })
     },
     selectModel: (payload: { provider: string; model: string; reasoningEffort?: string }) => {
       calls.select += 1
@@ -73,6 +76,15 @@ async function bench() {
       return Promise.resolve({ result: { ok: true as const, value: { selected: current } } })
     },
   } } })
+  // Whether the Host reports an adapter for the current route; the composer
+  // block follows this, never catalog membership.
+  let routable = true
+  const blocks = new Map<SessionId, { reason: string } | undefined>()
+  ctx.provide('conversation', {
+    blocks: {
+      set: (id: SessionId, block: { reason: string } | undefined) => { blocks.set(id, block) },
+    },
+  })
   let contribution: CommandContribution | undefined
   ctx.provide('command', {
     register(c: CommandContribution) {
@@ -115,6 +127,8 @@ async function bench() {
     hostCurrent: () => current,
     setHostCurrent: (target: ModelTarget) => { current = target },
     address: (id: SessionId) => { addressed.add(id) },
+    setRoutable: (next: boolean) => { routable = next },
+    blockOf: (key: string) => blocks.get(sid(key)),
   }
 }
 
@@ -217,6 +231,63 @@ describe('ui-model dual entry', () => {
     expect(face2.directory).not.toBe(face1.directory)
   })
 
+  it('blocks the composer only once the Host reports the route unservable', async () => {
+    const b = await bench()
+    b.mint('s1')
+    const face = b.seat().inject!(sid('s1'))
+
+    // Before the first load nothing is known. `null` is not `false`: a slow
+    // or unreachable Host must never lock a working composer.
+    expect(b.blockOf('s1')).toBeUndefined()
+    face.load()
+    await Promise.resolve()
+    await Promise.resolve()
+    expect(b.blockOf('s1')).toBeUndefined()
+
+    b.setRoutable(false)
+    b.ctx.emit('models/changed')
+    await Promise.resolve()
+    await Promise.resolve()
+    expect(b.blockOf('s1')?.reason).toBe(zh['blocked.composer'])
+
+    // Recovering clears it without a reload of the surface.
+    b.setRoutable(true)
+    b.ctx.emit('models/changed')
+    await Promise.resolve()
+    await Promise.resolve()
+    expect(b.blockOf('s1')).toBeUndefined()
+  })
+
+  it('never blocks on catalog membership alone', async () => {
+    const b = await bench()
+    b.mint('s1')
+    const face = b.seat().inject!(sid('s1'))
+    // A model the route serves but no longer advertises: the seat prompts for
+    // a selection, the composer stays usable. Blocking here would break a
+    // supported configuration (a narrowed `models` list over a live route).
+    b.setHostCurrent({ provider: 'deepseek-official', model: 'unlisted' })
+    face.load()
+    await Promise.resolve()
+    await Promise.resolve()
+    const snapshot = face.directory.getSnapshot()
+    expect(snapshot.groups.flatMap(group => group.models.map(model => model.id))).not.toContain('unlisted')
+    expect(b.blockOf('s1')).toBeUndefined()
+  })
+
+  it('clears its block when the session scope goes', async () => {
+    const b = await bench()
+    const scope = b.mint('s1')
+    b.setRoutable(false)
+    const face = b.seat().inject!(sid('s1'))
+    face.load()
+    await Promise.resolve()
+    await Promise.resolve()
+    expect(b.blockOf('s1')).toBeDefined()
+
+    await scope.fiber.dispose()
+    expect(b.blockOf('s1')).toBeUndefined()
+  })
+
   it('an unknown session fails loud at the seat inject', async () => {
     const b = await bench()
     expect(() => b.seat().inject!(sid('ghost'))).toThrow(/resolved no scope/)

packages/client/ui-model/tests/model-select.spec.tsx

@@ -32,6 +32,7 @@ const reasoning = {
 function state(overrides: Partial<ModelDirectoryState> = {}): ModelDirectoryState {
   return {
     current: { provider: 'deepseek-official', model: 'deepseek-v4-flash' },
+    routable: true,
     groups: [{
       id: 'deepseek-official',
       name: 'DeepSeek',