refactor(auth): unify Facebook and Google login into AuthPlatform class

Replace the separate FacebookLogin and GoogleLogin classes with a single
AuthPlatform class that takes a provider name ("facebook" | "google") as a
constructor argument. This consolidates duplicate OAuth sign-in logic behind
one entry point while preserving the existing NextAuth flow.

- Add new src/lib/auth/auth_platform.ts exporting AuthPlatform and
  AuthProvider type
- Update auth-facebook-panel.tsx and splash-button.tsx to use the new API
- Rename initialContext → initialState in the auth machine for consistency
- Update inline docs and comments to reference AuthPlatform

No behavioral change for end users; both providers still route through
NextAuth's signIn() with the same callbacks and cookies.

src/stores/chat/machine/chat-events.ts

@@ -0,0 +1,23 @@
+/**
+ * Chat 状态机：事件联合
+ *
+ * 事件名与原 Dart ChatEvent 对齐。
+ */
+export type ChatEvent =
+  | { type: "ChatInit" }
+  | { type: "ChatScreenVisible" }
+  | { type: "ChatScreenInvisible" }
+  | { type: "ChatSendMessage"; content: string }
+  | { type: "ChatSendImage"; imageBase64: string }
+  | { type: "ChatLoadMoreHistory" }
+  | {
+      type: "ChatAISentenceReceived";
+      index: number;
+      text: string;
+      total: number;
+      done: boolean;
+    }
+  | { type: "ChatWebSocketError"; errorMessage: string }
+  | { type: "ChatWebSocketConnected"; userId: string }
+  | { type: "ChatQuotaExceeded" }
+  | { type: "ChatAuthStatusChanged" };

src/stores/chat/machine/chat-machine.ts

@@ -0,0 +1,330 @@
+/**
+ * Chat 状态机（XState v5）
+ *
+ * 原始 Dart: lib/ui/chat/bloc/chat bloc + chat state + chat event
+ *
+ * 本轮迁移范围：
+ *   ✅ HTTP 流程（init / send message / load more history）
+ *   ✅ 上下文数据（messages / quota / 标志位）
+ *   ⏳ WebSocket 长生命周期 actor（fromCallback）—— 下轮处理
+ *
+ * 设计要点：
+ *   - 使用 XState v5 `setup({...}).createMachine({...})` 声明式 API
+ *   - HTTP 操作用 `fromPromise` actor（一次性 Promise）
+ *   - 保持事件类型名与原 Dart 一致，便于业务层迁移对照
+ *   - actions 全部 inline 在 setup() 中（确保类型推断正确）
+ */
+import { setup, fromPromise, assign } from "xstate";
+
+import type { UiMessage } from "@/models/chat/ui-message";
+import { chatRepository } from "@/data/repositories/chat_repository";
+import { ChatStorage } from "@/data/storage/chat/chat_storage";
+import { AuthStorage } from "@/data/storage/auth/auth_storage";
+import { formatDate } from "@/utils/date";
+import { Result } from "@/utils/result";
+
+import { ChatState, initialState } from "./chat-state";
+import type { ChatEvent } from "./machine/chat-events";
+
+/** 游客配额阈值（与 Dart `GuestChatQuota` 保持一致） */
+export const GuestChatQuota = {
+  warningThreshold: 5,
+  quotaExhausted: 0,
+} as const;
+
+// 重新导出 State / Event 类型，保持 machine 文件的公共 API 不变
+export type { ChatState } from "./chat-state";
+export { initialState } from "./chat-state";
+export type { ChatEvent } from "./machine/chat-events";
+
+// ============================================================
+// Helpers
+// ============================================================
+const PAGE_SIZE = 20;
+
+function localMessagesToUi(
+  records: ReadonlyArray<{
+    content: string;
+    role: string;
+    createdAt: string;
+  }>,
+): UiMessage[] {
+  return records.map((m) => ({
+    content: m.content,
+    isFromAI: m.role === "assistant",
+    date: m.createdAt,
+  }));
+}
+
+function mapQuotaResult(
+  r: Result<{ remaining: number } | null>,
+  fallback: number,
+): number {
+  if (r.success && r.data != null) return r.data.remaining;
+  return fallback;
+}
+
+function mapTotalQuotaResult(
+  r: Result<number | null>,
+  fallback: number,
+): number {
+  if (r.success && r.data != null) return r.data;
+  return fallback;
+}
+
+interface InitResult {
+  localMessages: UiMessage[];
+  isGuest: boolean;
+  guestRemainingQuota: number;
+  guestTotalQuota: number;
+}
+
+async function readInitData(): Promise<InitResult> {
+  const chatStorage = ChatStorage.getInstance();
+  const isGuest = !AuthStorage.getInstance().hasLoginToken();
+
+  const [dailyResult, totalResult, localResult] = await Promise.all([
+    chatStorage.getGuestDailyChatQuota(),
+    chatStorage.getGuestTotalQuota(),
+    isGuest ? chatRepository.getLocalMessages() : Promise.resolve(null),
+  ]);
+
+  return {
+    isGuest,
+    guestRemainingQuota: mapQuotaResult(
+      dailyResult as Result<{ remaining: number } | null>,
+      40,
+    ),
+    guestTotalQuota: mapTotalQuotaResult(
+      totalResult as Result<number | null>,
+      50,
+    ),
+    localMessages:
+      localResult && Result.isOk(localResult) && localResult.data
+        ? localMessagesToUi(localResult.data)
+        : [],
+  };
+}
+
+// ============================================================
+// Actors
+// ============================================================
+const chatInitActor = fromPromise<InitResult>(async () => readInitData());
+
+const sendMessageHttpActor = fromPromise<
+  { messages: UiMessage[] },
+  { content: string }
+>(async ({ input }) => {
+  const result = await chatRepository.sendMessage(input.content);
+  if (Result.isErr(result)) throw result.error;
+
+  // 拉取最新本地历史
+  const local = await chatRepository.getLocalMessages();
+  if (Result.isOk(local) && local.data) {
+    return { messages: localMessagesToUi(local.data) };
+  }
+  return { messages: [] };
+});
+
+const loadMoreHistoryActor = fromPromise<
+  { messages: UiMessage[]; hasMore: boolean; newOffset: number },
+  { offset: number }
+>(async ({ input }) => {
+  const result = await chatRepository.getHistory(PAGE_SIZE, input.offset);
+  if (Result.isErr(result)) throw result.error;
+
+  const page = localMessagesToUi(result.data.messages);
+  return {
+    messages: page,
+    hasMore: page.length >= PAGE_SIZE,
+    newOffset: input.offset + page.length,
+  };
+});
+
+// ============================================================
+// Machine
+// ============================================================
+export const chatMachine = setup({
+  types: {
+    context: {} as ChatState,
+    events: {} as ChatEvent,
+  },
+  actors: {
+    chatInit: chatInitActor,
+    sendMessageHttp: sendMessageHttpActor,
+    loadMoreHistory: loadMoreHistoryActor,
+  },
+  actions: {
+    appendUserMessage: assign(({ context, event }) => {
+      if (event.type !== "ChatSendMessage") return {};
+      return {
+        messages: [
+          ...context.messages,
+          {
+            content: event.content,
+            isFromAI: false,
+            date: formatDate(),
+          },
+        ],
+        isReplyingAI: true,
+      };
+    }),
+
+    appendUserImage: assign(({ context, event }) => {
+      if (event.type !== "ChatSendImage") return {};
+      return {
+        messages: [
+          ...context.messages,
+          {
+            content: "[Image]",
+            isFromAI: false,
+            date: formatDate(),
+            imageUrl: event.imageBase64,
+          },
+        ],
+        isReplyingAI: true,
+      };
+    }),
+
+    appendOrUpdateAISentence: assign(({ context, event }) => {
+      if (event.type !== "ChatAISentenceReceived") return {};
+      const messages = [...context.messages];
+      if (event.index === 0) {
+        messages.push({
+          content: event.text,
+          isFromAI: true,
+          date: formatDate(),
+        });
+      } else {
+        const last = messages[messages.length - 1];
+        if (last && last.isFromAI) {
+          messages[messages.length - 1] = {
+            ...last,
+            content: `${last.content} ${event.text}`,
+          };
+        }
+      }
+      return { messages, isReplyingAI: !event.done };
+    }),
+
+    appendSocketErrorMessage: assign(({ context }) => {
+      const messages = [
+        ...context.messages,
+        {
+          content: "Something went wrong. Try sending again?",
+          isFromAI: true,
+          date: formatDate(),
+        },
+      ];
+      return { messages, isReplyingAI: false };
+    }),
+
+    refreshAuthStatus: assign(() => ({
+      isGuest: !AuthStorage.getInstance().hasLoginToken(),
+    })),
+
+    incrementQuotaExceeded: assign(({ context }) => ({
+      quotaExceededTrigger: context.quotaExceededTrigger + 1,
+    })),
+  },
+}).createMachine({
+  id: "chat",
+  initial: "idle",
+  context: initialState,
+  states: {
+    idle: {
+      on: {
+        ChatInit: "initializing",
+        ChatScreenVisible: "ready",
+        ChatLoadMoreHistory: "loadingMoreHistory",
+        ChatSendMessage: {
+          guard: ({ event }) => event.content.trim().length > 0,
+          actions: "appendUserMessage",
+        },
+        ChatSendImage: {
+          actions: "appendUserImage",
+        },
+        ChatAuthStatusChanged: {
+          actions: "refreshAuthStatus",
+        },
+        ChatAISentenceReceived: {
+          actions: "appendOrUpdateAISentence",
+        },
+        ChatWebSocketError: {
+          actions: "appendSocketErrorMessage",
+        },
+        ChatQuotaExceeded: {
+          actions: "incrementQuotaExceeded",
+        },
+        ChatWebSocketConnected: {},
+      },
+    },
+
+    initializing: {
+      invoke: {
+        src: "chatInit",
+        onDone: {
+          target: "ready",
+          actions: assign({
+            messages: ({ event }) => event.output.localMessages,
+            isGuest: ({ event }) => event.output.isGuest,
+            guestRemainingQuota: ({ event }) => event.output.guestRemainingQuota,
+            guestTotalQuota: ({ event }) => event.output.guestTotalQuota,
+          }),
+        },
+        onError: {
+          target: "ready",
+        },
+      },
+    },
+
+    ready: {
+      on: {
+        ChatSendMessage: {
+          guard: ({ event }) => event.content.trim().length > 0,
+          actions: "appendUserMessage",
+        },
+        ChatSendImage: {
+          actions: "appendUserImage",
+        },
+        ChatLoadMoreHistory: "loadingMoreHistory",
+        ChatScreenInvisible: "idle",
+        ChatAuthStatusChanged: {
+          actions: "refreshAuthStatus",
+        },
+        ChatAISentenceReceived: {
+          actions: "appendOrUpdateAISentence",
+        },
+        ChatWebSocketError: {
+          actions: "appendSocketErrorMessage",
+        },
+        ChatQuotaExceeded: {
+          actions: "incrementQuotaExceeded",
+        },
+        ChatWebSocketConnected: {},
+      },
+    },
+
+    loadingMoreHistory: {
+      invoke: {
+        src: "loadMoreHistory",
+        input: ({ context }) => ({ offset: context.historyOffset }),
+        onDone: {
+          target: "ready",
+          actions: assign(({ context, event }) => ({
+            messages: [...event.output.messages, ...context.messages],
+            isLoadingMore: false,
+            hasMore: event.output.hasMore,
+            historyOffset: event.output.newOffset,
+          })),
+        },
+        onError: {
+          target: "ready",
+          actions: assign({ isLoadingMore: false }),
+        },
+      },
+    },
+  },
+});
+
+export type ChatMachine = typeof chatMachine;

src/stores/chat/machine/chat-state.ts

@@ -0,0 +1,30 @@
+/**
+ * Chat 状态机：State 形状 + 初始值
+ *
+ * 注：GuestChatQuota 仍位于 chat-machine.ts（属于业务常量，与上下文配对紧密）。
+ */
+import type { UiMessage } from "@/models/chat/ui-message";
+
+export interface ChatState {
+  messages: UiMessage[];
+  isReplyingAI: boolean;
+  isGuest: boolean;
+  guestRemainingQuota: number;
+  guestTotalQuota: number;
+  quotaExceededTrigger: number;
+  isLoadingMore: boolean;
+  hasMore: boolean;
+  historyOffset: number;
+}
+
+export const initialState: ChatState = {
+  messages: [],
+  isReplyingAI: false,
+  isGuest: true,
+  guestRemainingQuota: 40,
+  guestTotalQuota: 50,
+  quotaExceededTrigger: 0,
+  isLoadingMore: false,
+  hasMore: true,
+  historyOffset: 0,
+};