Merge remote-tracking branch 'origin/master' into worktree/web-multimodal-image-input

# Conflicts:
#	packages/client/runtime/README.i18n.yaml
#	packages/client/ui-conversation/README.i18n.yaml
#	packages/client/ui-conversation/README.md
#	packages/client/ui-conversation/README.zh.md
#	packages/client/ui-conversation/src/client/chat/MessageItem.tsx

packages/client/test-runtime/src/fixtures.ts

@@ -46,7 +46,6 @@ export function conversationSnapshot(sessionId: SessionId): ConversationSnapshot
   return {
     sessionId,
     nodes: [],
-    foldDegraded: false,
     partial: null,
     runningCalls: [],
     codeDispatches: new Map(),

packages/client/test-runtime/src/index.ts

@@ -38,6 +38,7 @@ export { TestWorkspaces } from './workspaces.ts'
 export { conversationSnapshot, workspaceListState } from './fixtures.ts'
 export type { SessionBehaviorOverrides, SessionFixture, Stabilizer } from './fixtures.ts'
 export { makeTranslate } from './translate.ts'
+export { usePinnedBrowserLanguages } from './locale-env.ts'
 
 /** Erased register face for the internal root call (the public declare seam holds the typing). */
 type ErasedRegister = (options: object, component: unknown) => () => void

packages/client/test-runtime/src/locale-env.ts

@@ -0,0 +1,29 @@
+/**
+ * Browser-language pin for specs that assert localized copy. A fresh
+ * LocaleService with no stored preference opens in the language `navigator`
+ * asks for, and jsdom reports the runner's own (`en-US`) — so a spec asserting
+ * the product's Chinese copy states the browser it assumes instead of
+ * inheriting the machine's.
+ */
+import { afterEach, beforeEach } from 'vitest'
+
+/**
+ * Pin `navigator.languages`/`navigator.language` for every test in the
+ * calling file (or describe block), restoring the environment's own values
+ * afterwards. Call at suite level, like the other vitest hooks.
+ * @param primary - most preferred BCP 47 tag; also becomes `navigator.language`.
+ * @param rest - further tags in preference order.
+ */
+export function usePinnedBrowserLanguages(primary: string, ...rest: string[]): void {
+  beforeEach(() => {
+    Object.defineProperty(navigator, 'languages', { value: [primary, ...rest], configurable: true })
+    Object.defineProperty(navigator, 'language', { value: primary, configurable: true })
+  })
+  afterEach(() => {
+    // Deleting the own properties uncovers the environment's own accessors
+    // again (Navigator declares both readonly, hence the erased receiver).
+    const own = navigator as unknown as Record<string, unknown>
+    delete own.languages
+    delete own.language
+  })
+}