fix(web-ui): translate the deck list load error and test Settings

web-ui/messages/en.json

@@ -420,7 +420,8 @@
     "bulkDeleteFailed": "{count, plural, one {# deck} other {# decks}} could not be deleted.",
     "bulkDeleteDescriptionLocal": "The selected deck folders will be deleted immediately. This action cannot be undone.",
     "errorUpdateVisibility": "Failed to update visibility.",
-    "errorDeleteDeck": "Failed to delete deck."
+    "errorDeleteDeck": "Failed to delete deck.",
+    "errorLoadDecks": "Failed to load decks."
   },
   "mcp": {
     "connected": "Connected: {names}",

web-ui/messages/ja.json

@@ -420,7 +420,8 @@
     "bulkDeleteFailed": "{count, plural, other {# 件のデッキを削除できませんでした。}}",
     "bulkDeleteDescriptionLocal": "選択したデッキのフォルダを即時に削除します。この操作は元に戻せません。",
     "errorUpdateVisibility": "公開範囲を更新できませんでした",
-    "errorDeleteDeck": "デッキを削除できませんでした"
+    "errorDeleteDeck": "デッキを削除できませんでした",
+    "errorLoadDecks": "デッキを読み込めませんでした"
   },
   "mcp": {
     "connected": "接続済み: {names}",

web-ui/src/components/Settings.test.tsx

@@ -0,0 +1,72 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT-0
+/** Settings (local): agent selection toasts are translated and a failed save rolls back. */
+
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest"
+import { cleanup, fireEvent, screen, waitFor } from "@testing-library/react"
+import { toast } from "sonner"
+import { renderWithIntl } from "@/test/renderWithIntl"
+
+vi.mock("@/lib/mode", () => ({ IS_LOCAL: true }))
+vi.mock("sonner", () => ({ toast: { success: vi.fn(), error: vi.fn() } }))
+vi.mock("@/services/localService", () => ({
+  getAgentDefinitions: vi.fn(),
+  listLocalModels: vi.fn(),
+  updateAgentSelection: vi.fn(),
+}))
+
+import { getAgentDefinitions, listLocalModels, updateAgentSelection } from "@/services/localService"
+import { Settings } from "./Settings"
+
+// jsdom has no scrollIntoView; cmdk and ModelPicker call it.
+beforeAll(() => {
+  Element.prototype.scrollIntoView = vi.fn()
+})
+
+const AGENTS = [
+  { fileName: "a.json", name: "Agent A", description: "" },
+  { fileName: "b.json", name: "Agent B", description: "" },
+]
+
+async function pickOrchestrator(locale: "en" | "ja") {
+  renderWithIntl(<Settings open onOpenChange={() => {}} />, { locale })
+  const trigger = await screen.findByLabelText("Select orchestrator agent")
+  await waitFor(() => expect(trigger.textContent).toContain("Agent A"))
+  fireEvent.click(trigger)
+  fireEvent.click(screen.getByRole("option", { name: /Agent B/ }))
+  return trigger
+}
+
+describe("Settings (local) — agent selection", () => {
+  beforeEach(() => {
+    vi.mocked(getAgentDefinitions).mockResolvedValue({
+      agents: AGENTS,
+      selection: { orchestrator: "a.json", composer: "a.json", style: "a.json", translate: "a.json" },
+    })
+    vi.mocked(listLocalModels).mockResolvedValue([])
+  })
+
+  afterEach(() => {
+    cleanup()
+    vi.clearAllMocks()
+  })
+
+  it("shows the translated toast after saving", async () => {
+    vi.mocked(updateAgentSelection).mockResolvedValue(undefined)
+    const trigger = await pickOrchestrator("ja")
+    await waitFor(() => expect(toast.success).toHaveBeenCalledWith(
+      "orchestrator エージェントを更新しました",
+      { description: "Agent B を使用します。次のチャットから反映され、現在のチャットには影響しません。" },
+    ))
+    expect(updateAgentSelection).toHaveBeenCalledWith({ orchestrator: "b.json" })
+    expect(trigger.textContent).toContain("Agent B")
+  })
+
+  it("rolls the selection back and shows the translated error when the save fails", async () => {
+    vi.mocked(updateAgentSelection).mockRejectedValue(new Error("HTTP 500"))
+    const trigger = await pickOrchestrator("ja")
+    await waitFor(() => expect(toast.error).toHaveBeenCalledWith("orchestrator エージェントを更新できませんでした"))
+    expect(toast.success).not.toHaveBeenCalled()
+    await waitFor(() => expect(trigger.textContent).toContain("Agent A"))
+  })
+})

web-ui/src/hooks/useDeckList.test.ts

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: MIT-0
 
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest"
-import { act, renderHook } from "@testing-library/react"
+import { act, renderHook, waitFor } from "@testing-library/react"
 import { toast } from "sonner"
 import { intlWrapper } from "@/test/renderWithIntl"
 import en from "../../messages/en.json"
@@ -109,4 +109,15 @@ describe("useDeckList — translated action errors", () => {
     await act(async () => { await result.current.handleToggleVisibility("d1", "public") })
     expect(toast.error).toHaveBeenCalledWith(expected)
   })
+
+  it.each([
+    ["en", en.decksPage.errorLoadDecks],
+    ["ja", "デッキを読み込めませんでした"],
+  ] as const)("shows the %s banner instead of the raw error when the list cannot load", async (locale, expected) => {
+    api.listDecks.mockRejectedValueOnce(new Error("Failed to list decks: 500"))
+    vi.spyOn(console, "error").mockImplementation(() => {})
+    const { result } = renderHook(() => useDeckList("token", true, null), { wrapper: intlWrapper(locale) })
+    await waitFor(() => expect(result.current.loading).toBe(false))
+    expect(result.current.error).toBe(expected)
+  })
 })

web-ui/src/hooks/useDeckList.ts

@@ -51,7 +51,8 @@ export function useDeckList(
   const [favoriteIds, setFavoriteIds] = useState<Set<string>>(new Set())
   const [activeListTab, setActiveListTab] = useState<"mine" | "favorites" | "public">("mine")
   const [loading, setLoading] = useState(true)
-  const [error, setError] = useState<string | null>(null)
+  /** The first list load failed; translated at render (the raw error goes to the console). */
+  const [loadFailed, setLoadFailed] = useState(false)
   const [deleteTarget, setDeleteTarget] = useState<DeckSummary | null>(null)
   const [bulkDeleteTargets, setBulkDeleteTargets] = useState<DeckSummary[] | null>(null)
   const [bulkProgress, setBulkProgress] = useState<{ done: number; total: number } | null>(null)
@@ -94,7 +95,8 @@ export function useDeckList(
         setFavoriteDecks(favDecks)
       } catch (err) {
         if (!initialLoadDone.current) {
-          setError(err instanceof Error ? err.message : "Failed to load decks")
+          console.error("Failed to load decks", err)
+          setLoadFailed(true)
         }
       } finally {
         initialLoadDone.current = true
@@ -263,6 +265,8 @@ export function useDeckList(
     : activeListTab === "favorites" ? favoriteDecks
     : publicDecks
 
+  const error = loadFailed ? t("errorLoadDecks") : null
+
   return {
     decks, tabDecks, favoriteIds, activeListTab, setActiveListTab,
     loading, error, deleteTarget, setDeleteTarget,