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.

apps/web/tests/default-model.e2e.ts

@@ -4,11 +4,14 @@
 // a route keeps deriving from its own log — the tier order the gateway
 // resolves on every read.
 // Zero model calls: the switch is settings/llm-domain traffic only, so there
-// is no fixture and a stray stream would fail loud on the open seam. A second
-// route is declared host-side (not through the UI, which has its own
-// scenario) purely so the picker has somewhere to switch to: the keyless
-// replay catalog publishes a single model.
+// is no fixture and a stray stream would fail loud on the open seam. Both
+// routes are declared host-side (not through the UI, which has its own
+// scenario) through the pi-ai adapter the shipped tree already mounts: a
+// fixture-less scaffold registers no adapter at all, so the routes the
+// picker offers — and the one the composer must start on — have to come from
+// somewhere, and settings profiles are the product's own way to add them.
 import { readFile } from 'node:fs/promises'
+import { fileURLToPath } from 'node:url'
 import { join } from 'node:path'
 import type { Browser, Page } from 'playwright'
 import { chromium } from 'playwright'
@@ -18,7 +21,13 @@ import { settingsNamespace } from '@deepseek-ai/dsh-settings'
 import { launchWebScaffold, watchConsole, type WebScaffold } from './scaffold.ts'
 import { ZH_BROWSER_LOCALE, connectFreshWorkspaceZh, saveFailureShot } from './support.ts'
 
-/** The route declared for this scenario, and the model the switch lands on. */
+/** Points the shipped `api-gateway` default at this scenario's own route. */
+const OVERLAY = fileURLToPath(new URL('./default-model.overlay.yml', import.meta.url))
+
+/** The route this scenario starts on, patched over the shipped default. */
+const START_ROUTE = 'origin-gateway'
+const START_MODEL = 'origin-large'
+/** The route the switch lands on, which then becomes the saved default. */
 const ROUTE = 'acme-gateway'
 const MODEL = 'acme-large'
 
@@ -49,12 +58,19 @@ describe('web e2e: the composer model switch is the default for later sessions',
   }
 
   beforeAll(async () => {
-    scaffold = await launchWebScaffold({})
-    // A second route so the picker has two models. Declared through the
-    // settings seam rather than the Models page: this scenario is about the
-    // composer, and the declaring flow is covered by models-settings.e2e.
+    scaffold = await launchWebScaffold({ extraOverlayPath: OVERLAY })
+    // Two routes so the picker has somewhere to start and somewhere to go.
+    // Declared through the settings seam rather than the Models page: this
+    // scenario is about the composer, and the declaring flow is covered by
+    // models-settings.e2e.
     await scaffold.ctx.settings.update(settingsNamespace('llm-pi-ai'), {
       providers: {
+        [START_ROUTE]: {
+          displayName: 'Origin Gateway',
+          api: 'openai-completions',
+          baseURL: 'https://gateway.origin.example/v1',
+          models: [{ id: START_MODEL, name: 'Origin Large' }],
+        },
         [ROUTE]: {
           displayName: 'Acme Gateway',
           api: 'openai-completions',
@@ -84,7 +100,7 @@ describe('web e2e: the composer model switch is the default for later sessions',
     // leaves behind: its own logged route.
     const loggedId = await createSession('default-model-logged')
     scaffold.ctx.sessions.get(SessionId(loggedId))?.append('request/header', {
-      header: { config: { provider: 'deepseek-official', model: 'deepseek-v4-flash' } },
+      header: { config: { provider: START_ROUTE, model: START_MODEL } },
       reason: 'initial',
     })
 
@@ -108,8 +124,35 @@ describe('web e2e: the composer model switch is the default for later sessions',
     expect(await currentOf(await createSession('default-model-after')))
       .toEqual({ provider: ROUTE, model: MODEL })
     // ...while the one holding a logged route keeps deriving from its log.
-    expect(await currentOf(loggedId))
-      .toEqual({ provider: 'deepseek-official', model: 'deepseek-v4-flash' })
+    expect(await currentOf(loggedId)).toEqual({ provider: START_ROUTE, model: START_MODEL })
+    expect(tripwire.pageErrors).toEqual([])
+  }, 60_000)
+
+  it('goes inert when the route the default names stops being served', async () => {
+    onTestFailed(() => saveFailureShot(page, 'web-e2e-default-model-blocked'))
+    const box = page.locator('textarea[data-input-phase], textarea').first()
+    await expect.poll(async () => box.isEnabled(), { timeout: 10_000 }).toBe(true)
+
+    // What removing the provider on the Models page leaves behind: the saved
+    // default still names the route, and nothing serves it any more.
+    // `replace`, not `update`: a merge patch of `{providers: {}}` leaves every
+    // stored profile in place.
+    await scaffold.ctx.settings.replace(settingsNamespace('llm-pi-ai'), { providers: {} })
+
+    await expect.poll(async () => box.isEnabled(), { timeout: 15_000 }).toBe(false)
+    expect(await box.getAttribute('placeholder')).toBe('当前模型不可用，请先选择模型')
+
+    // The block is an affordance; the refusal is the Host's. A client that
+    // never disabled anything still cannot start a turn on a dead route.
+    const refused = await scaffold.ctx.apiProxy.sessions.prompt({
+      rpcId: 'default-model-refused' as never,
+      payload: {
+        sessionId: SessionId(await createSession('default-model-refusal')),
+        mode: 'queue' as const,
+        content: [{ type: 'text' as const, text: 'hi' }],
+      },
+    })
+    expect(refused.result).toMatchObject({ ok: false, error: { code: 'model-unavailable' } })
     expect(tripwire.pageErrors).toEqual([])
   }, 60_000)
 })

apps/web/tests/default-model.overlay.yml

@@ -0,0 +1,8 @@
+# The fixture-less web scaffold registers no adapter, so the shipped
+# deepseek-official default would be a route nothing serves — which the
+# composer now correctly refuses to type into. This scenario declares its own
+# pi-ai routes and starts the default on one of them.
+- id: api-gateway
+  config:
+    provider: origin-gateway
+    model: origin-large

apps/web/tests/message-actions.e2e.ts

@@ -126,7 +126,7 @@ describe('web e2e: message IconActions and clocks on settled history', () => {
 
   it.skipIf(MODE === 'record')('matches the conversation aria golden with IconActions and clocks', async () => {
     onTestFailed(() => saveFailureShot(page, 'web-e2e-message-actions-aria'))
-    await page.getByRole('button', { name: 'Select model', exact: true })
+    await page.getByRole('button', { name: /^Select model, current/ })
       .waitFor({ timeout: 10_000 })
     // Keep a footer focused so opacity-hidden actions stay in the a11y tree
     // as an active/focused control during the capture.

apps/web/tests/scaffold.ts

@@ -45,6 +45,10 @@ import {
   WELCOME_NOTICE_ACK_FIELD, WELCOME_NOTICE_SETTINGS_NAMESPACE, WELCOME_NOTICE_VERSION,
 } from '@deepseek-ai/dsh-client-ui-settings-general'
 import { settingsNamespace } from '@deepseek-ai/dsh-settings'
+import { LlmAdapter } from '@deepseek-ai/dsh-llm'
+import type {
+  LlmModelInfo, LlmProviderInfo, LlmResolvedModelInfo, StreamChunk,
+} from '@deepseek-ai/dsh-llm'
 import type { ReplayHandle } from '@deepseek-ai/dsh-llm-replay'
 import { installLlmReplay, parseSessionLog } from '@deepseek-ai/dsh-llm-replay'
 import SessionStore, {
@@ -93,6 +97,46 @@ const REPLAY_PROVIDERS = [{
   models: [{ id: 'deepseek-v4-flash', name: 'DeepSeek-V4-Flash', contextWindow: 128_000 }],
 }]
 
+/**
+ * The routes a shipped composition always has, with no ability to stream.
+ * A fixture-less keyless scenario issues no model calls, but its tree must
+ * still answer `listProviders()` — surfaces legitimately gate on whether any
+ * adapter serves a session's route, and an empty registry is a test artifact,
+ * not a product state.
+ */
+class RouteOnlyAdapter extends LlmAdapter {
+  constructor(private readonly providers: typeof REPLAY_PROVIDERS) {
+    super()
+  }
+
+  override providerInfo(provider: string): LlmProviderInfo {
+    return { id: provider, name: this.providers.find(entry => entry.id === provider)?.name ?? provider }
+  }
+
+  override listModels(provider: string): Promise<readonly LlmModelInfo[]> {
+    return Promise.resolve((this.providers.find(entry => entry.id === provider)?.models ?? [])
+      .map(model => ({ provider, id: model.id, name: model.name })))
+  }
+
+  override resolveModel(provider: string, model: string): Promise<LlmResolvedModelInfo> {
+    const listed = this.providers.find(entry => entry.id === provider)?.models
+      .find(entry => entry.id === model)
+    return Promise.resolve({
+      provider,
+      id: model,
+      name: listed?.name ?? model,
+      ...listed?.contextWindow === undefined ? {} : { contextWindow: listed.contextWindow },
+    })
+  }
+
+  override async *stream(): AsyncIterable<StreamChunk> {
+    throw new Error(
+      'web e2e scaffold: a model call was issued by a scenario that declared no replay fixture'
+      + ' — pass replayFixture, or keep the scenario free of model calls',
+    )
+  }
+}
+
 function replayProviders(contextWindow: number | undefined): typeof REPLAY_PROVIDERS {
   if (contextWindow === undefined) return REPLAY_PROVIDERS
   return REPLAY_PROVIDERS.map(provider => ({
@@ -390,6 +434,16 @@ export async function launchWebScaffold(options: LaunchOptions = {}): Promise<We
         ...(options.replayChildFixtures === undefined ? {} : { childFiles: options.replayChildFixtures }),
         ...(options.paceMs === undefined ? {} : { paceMs: options.paceMs }),
       })
+    } else if (mode !== 'record' && options.deepSeekMissingCredential !== true) {
+      // No fixture and no shipped adapter would leave the tree with ZERO
+      // provider routes — a state no product composition has, and one the
+      // composer now correctly refuses to type into. Register the same routes
+      // a fixture would, with streaming that still fails loud: the scenario
+      // issues no model calls, and one that slipped in must not pass quietly.
+      ctx.effect(() => ctx.llm.registerAdapter(
+        replayProviders(options.replayContextWindow).map(provider => provider.id),
+        new RouteOnlyAdapter(replayProviders(options.replayContextWindow)),
+      ), 'web e2e scaffold: route-only adapter')
     }
   } catch (error) {
     if (process.cwd() !== originalCwd) process.chdir(originalCwd)

apps/web/tests/seeded-history.e2e.ts

@@ -280,10 +280,10 @@ describe('web e2e: seeded history renders through cold resume', () => {
 
   it.skipIf(MODE === 'record')('matches the historical conversation aria golden', async () => {
     onTestFailed(() => saveFailureShot(page, 'web-e2e-seeded-aria'))
-    // This scenario deliberately leaves the LLM seam open to prove zero
-    // model calls. History still restores the routed id, but without an
-    // advertised catalog row the selector prompts for a listed replacement.
-    await page.getByRole('button', { name: 'Select model', exact: true })
+    // This scenario issues zero model calls — the scaffold's route-only
+    // adapter serves the catalog and refuses to stream — so history restores
+    // the routed id and the seat resolves it against an advertised row.
+    await page.getByRole('button', { name: /^Select model, current/ })
       .waitFor({ timeout: 10_000 })
     const snapshot = (await captureStableAria(page, '[class*="centerCol"]', scaffold.workspaceCwd))
       .split(SEED_ID).join('{{seededId}}')

apps/web/tests/snapshots/bash-abort-row/ui.expected.md

@@ -23,8 +23,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 1 steps LLM {{duration}} · Tool call {{duration}} TTFT avg {{duration}} · {{throughput}} tok/s Cache hit 0% Input 10 tok · Output 10 tok

apps/web/tests/snapshots/lifecycle-chrome/plan-active.expected.md

@@ -30,8 +30,8 @@
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
 - button "Plan mode on, press to turn off": Plan
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: Details

apps/web/tests/snapshots/markdown-cjk-strong/ui.expected.md

@@ -42,8 +42,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 1 steps LLM {{duration}} Input 0 tok · Output 0 tok

apps/web/tests/snapshots/markdown-images/ui.expected.md

@@ -21,8 +21,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 1 steps LLM {{duration}} Input 0 tok · Output 0 tok

apps/web/tests/snapshots/markdown-inline-code-links/ui.expected.md

@@ -33,8 +33,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 1 steps LLM {{duration}} Input 0 tok · Output 0 tok

apps/web/tests/snapshots/math-rendering/ui.expected.md

@@ -37,8 +37,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 1 steps LLM {{duration}} Input 0 tok · Output 0 tok

apps/web/tests/snapshots/message-actions/ui.expected.md

@@ -45,8 +45,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 2 turns · 3 steps LLM {{duration}} · Tool call {{duration}} TTFT avg {{duration}} · {{throughput}} tok/s Cache hit 98% Input 7.8K tok · Output 103 tok

apps/web/tests/snapshots/seeded-history/command-row.expected.md

@@ -44,8 +44,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Read Only"': Read Only
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 2 steps LLM {{duration}} · Tool call {{duration}} TTFT avg {{duration}} · {{throughput}} tok/s Cache hit 98% Input 15.8K tok · Output 135 tok

apps/web/tests/snapshots/seeded-history/ui.expected.md

@@ -42,8 +42,8 @@
 - button "Commands":
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: 1 turns · 2 steps LLM {{duration}} · Tool call {{duration}} TTFT avg {{duration}} · {{throughput}} tok/s Cache hit 98% Input 15.8K tok · Output 135 tok