feat(client): typed locale standard seat in the slot framework

Registrations declare a dictionary namespace (locale: NS) and the renderer
synthesizes a typed t prop for the entry's component from the installed
LocaleFace; the seat binding is re-derived per locale revision, so a language
switch hands out fresh t references and memoized consumers re-render through
ordinary shallow comparison. LocaleNamespaceMap is the declare-merge table
(namespace -> dictionary key union); TranslateNS<'ns'> is the
namespace-addressed translate type (namespace keys plus the shared common
vocabulary), carried by the t seat and by the locale service's typed bind.

LocaleService implements the face (lookup ns -> common -> zh -> key,
revision-carrying snapshots with subscriber isolation) and installs it
through the boot-once slots.installLocale seam, mirroring the renderer
install. The typed register(ns, {zh, en}) overload checks each dictionary
against the namespace's key union and requires every shipped locale, so a
missing or extra key and an unbalanced translation are compile errors.
Dictionary registration bumps the face revision without emitting
locale/change — the event now means exactly 'the active locale switched',
so registration-heavy boot cannot storm event listeners.

packages/client/ui-sidebar/tests/apply.spec.tsx

@@ -2,6 +2,7 @@
 import { Context } from 'cordis'
 import { describe, expect, it, vi } from 'vitest'
 import { SlotsService } from '@deepseek-ai/dsh-client-runtime/client'
+import { LocaleService } from '@deepseek-ai/dsh-client-locale/client'
 import { apply, inject } from '@deepseek-ai/dsh-client-ui-sidebar/client'
 import type { SidebarRootInjected } from '@deepseek-ai/dsh-client-ui-sidebar/client'
 
@@ -14,6 +15,7 @@ async function bench(declare = true) {
   ctx.provide('layout', layout)
   ctx.provide('sessions', sessions as never)
   ctx.provide('workspaces', workspaces as never)
+  ctx.provide('locale', new LocaleService(ctx))
   const slots = ctx.get('slots') as SlotsService
   if (declare) {
     slots.register(
@@ -26,7 +28,7 @@ async function bench(declare = true) {
 
 describe('ui-sidebar apply', () => {
   it('declares only the services it uses', () => {
-    expect(inject).toEqual(['slots', 'layout', 'sessions', 'workspaces'])
+    expect(inject).toEqual(['slots', 'layout', 'sessions', 'workspaces', 'locale'])
   })
 
   it('registers the shell and declares the browsing-region hole', async () => {
@@ -34,6 +36,8 @@ describe('ui-sidebar apply', () => {
     await b.ctx.plugin({ inject: [...inject], apply }).await()
     expect(b.slots.entries('sidebar')).toHaveLength(1)
     expect(b.slots.spec('sidebar.workspaces')).toEqual({ kind: 'single', scope: 'root' })
+    // Copy rides the standard locale seat, not the inject face.
+    expect(b.slots.entries('sidebar')[0]!.locale).toBe('sidebar')
     const injected = (b.slots.entries('sidebar')[0]!.inject as () => SidebarRootInjected)()
     expect(Object.keys(injected)).toEqual(['startSession', 'toggleSidebar'])
     // Both arms delegate to the runtime's shared New Session action.

packages/client/ui-sidebar/tests/sidebar-root.spec.tsx

@@ -3,6 +3,11 @@ import { afterEach, describe, expect, it, vi } from 'vitest'
 import { cleanup, fireEvent, render, screen } from '@testing-library/react'
 import type { SidebarRootComponentProps, SidebarSectionOwnerProps, SidebarSettingsOwnerProps } from '../src/client/contract/slots.ts'
 import { SidebarRoot } from '../src/client/SidebarRoot.tsx'
+import { en } from '../src/client/locales.ts'
+
+// English-dictionary translate stub: the shell renders the same copy the
+// assertions below query by accessible name.
+const t: SidebarRootComponentProps['t'] = key => (en as Record<string, string>)[key] ?? key
 
 afterEach(() => {
   cleanup()
@@ -23,7 +28,7 @@ function mountShell({ collapsed = false, width = 300 }: { collapsed?: boolean; w
     <SidebarRoot
       collapsed={current.collapsed} width={current.width}
       useSessions={neverHook} useWorkspaces={neverHook}
-      startSession={startSession} toggleSidebar={toggleSidebar}
+      startSession={startSession} toggleSidebar={toggleSidebar} t={t}
       renderSlot={((key: string, owner: SidebarSectionOwnerProps | SidebarSettingsOwnerProps) => {
         if (key === 'sidebar.settings') {
           settingsOwner = owner

packages/client/ui-sidebar/tests/sidebar-snapshot.spec.tsx

@@ -11,6 +11,7 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
 import { cleanup, waitFor } from '@testing-library/react'
 import { SlotTestRuntime } from '@deepseek-ai/dsh-client-test-runtime'
+import { LocaleService } from '@deepseek-ai/dsh-client-locale/client'
 import { apply, inject } from '@deepseek-ai/dsh-client-ui-sidebar/client'
 
 afterEach(cleanup)
@@ -18,6 +19,12 @@ afterEach(cleanup)
 async function bench() {
   const runtime = await SlotTestRuntime.create()
   runtime.provide('layout', { toggleSidebar: vi.fn() })
+  // English locale pins the snapshots to the copy they were recorded with;
+  // the installed face backs the entry's standard `t` seat.
+  const locale = new LocaleService(runtime.ctx)
+  locale.setLocale('en')
+  runtime.provide('locale', locale)
+  runtime.slots.installLocale(locale)
   await runtime.declare({ 'sidebar': { kind: 'single', scope: 'root' } })
   await runtime.mount({ inject: [...inject], apply })
   return runtime