diff --git a/apps/portal-shell/src/lib/api/errors.ts b/apps/portal-shell/src/lib/api/errors.ts
new file mode 100644
index 0000000..ce995d1
--- /dev/null
+++ b/apps/portal-shell/src/lib/api/errors.ts
@@ -0,0 +1,29 @@
+/**
+ * API 层统一错误类型
+ *
+ * 所有 lib/api/ 函数抛出的错误都用 ApiError 包装，
+ * 便于 widget 层按 code 分类处理（401 跳登录、403 显示无权限等）。
+ *
+ * 关联：spec §6.1
+ */
+export type GraphQLErrorCode =
+  | "UNAUTHORIZED"
+  | "FORBIDDEN"
+  | "NOT_FOUND"
+  | "VALIDATION_ERROR"
+  | "QUERY_DEPTH_EXCEEDED"
+  | "QUERY_COMPLEXITY_EXCEEDED"
+  | "PERSISTED_QUERY_NOT_FOUND"
+  | "INTERNAL_ERROR";
+
+export class ApiError extends Error {
+  constructor(
+    message: string,
+    public readonly code: GraphQLErrorCode,
+    public readonly statusCode: number = 500,
+    public readonly fields?: string[],
+  ) {
+    super(message);
+    this.name = "ApiError";
+  }
+}
diff --git a/apps/portal-shell/src/lib/api/index.ts b/apps/portal-shell/src/lib/api/index.ts
new file mode 100644
index 0000000..5aa48fe
--- /dev/null
+++ b/apps/portal-shell/src/lib/api/index.ts
@@ -0,0 +1,10 @@
+/**
+ * API 层统一出口
+ *
+ * widget 通过 `import { useParentChildren } from "@/lib/api"` 调用。
+ * 各 domain 文件在 M2 阶段逐步加入。
+ *
+ * 关联：spec §2.2
+ */
+export * from "./errors";
+export * from "./types";
diff --git a/apps/portal-shell/src/lib/api/internal.ts b/apps/portal-shell/src/lib/api/internal.ts
new file mode 100644
index 0000000..86d4ed9
--- /dev/null
+++ b/apps/portal-shell/src/lib/api/internal.ts
@@ -0,0 +1,18 @@
+/**
+ * API 层共享工具
+ *
+ * 错误归一化：把 ApolloError 转为 ApiError，
+ * 让 widget 层可以用 instanceof ApiError 判断。
+ *
+ * 关联：spec §6.2
+ */
+import type { ApolloError } from "@apollo/client";
+import { ApiError, type GraphQLErrorCode } from "./errors";
+
+export function normalizeError(error: ApolloError): ApiError {
+  const gqlError = error.graphQLErrors?.[0];
+  const code = (gqlError?.extensions?.code ??
+    "INTERNAL_ERROR") as GraphQLErrorCode;
+  const statusCode = (gqlError?.extensions?.statusCode ?? 500) as number;
+  return new ApiError(gqlError?.message ?? error.message, code, statusCode);
+}
diff --git a/apps/portal-shell/src/lib/api/types.ts b/apps/portal-shell/src/lib/api/types.ts
new file mode 100644
index 0000000..c373c7f
--- /dev/null
+++ b/apps/portal-shell/src/lib/api/types.ts
@@ -0,0 +1,29 @@
+/**
+ * API 层共享类型
+ *
+ * 跨 domain 复用的分页、筛选等通用类型。
+ * 领域专属类型（如 ChildSummary）放在各自的 domain 文件。
+ *
+ * 关联：spec §2.2
+ */
+export interface Pagination {
+  limit: number;
+  offset: number;
+}
+
+export interface PaginatedResult<T> {
+  items: T[];
+  total: number;
+}
+
+export interface UseQueryResult<TData> {
+  data: TData | undefined;
+  loading: boolean;
+  error: unknown;
+  refetch: () => Promise<unknown>;
+}
+
+export interface UseMutationResult {
+  loading: boolean;
+  error: unknown;
+}