修复资产计费边界风险

资产生成预扣费改为 fail-closed，避免钱包异常时继续调用外部生成

新增钱包退款 outbox，退款失败时本地落盘并后台重放

拼图首图后台任务改用 SpacetimeDB claim 表实现跨实例互斥

计费 ledger id 统一绑定 request_id，并让前端重试复用 x-request-id

同步 SpacetimeDB bindings、后端架构文档和 Hermes 决策记录

src/services/apiClient.ts

@@ -40,6 +40,8 @@ export type ApiRequestOptions = {
   notifyAuthStateChange?: boolean;
   // 推荐页自动加载作品这类局部后台请求失败时，只应让当前卡片报错，不应清空全局登录态。
   clearAuthOnUnauthorized?: boolean;
+  // 同一次业务请求在客户端重试时复用 request id，后端据此做计费幂等。
+  requestId?: string;
 };
 
 export const BACKGROUND_AUTH_REQUEST_OPTIONS = {
@@ -99,6 +101,22 @@ function normalizeHeaders(headers?: HeadersInit) {
   return nextHeaders;
 }
 
+function buildClientRequestId() {
+  const randomId =
+    typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function'
+      ? crypto.randomUUID()
+      : `${Date.now().toString(36)}-${Math.random().toString(36).slice(2)}`;
+  return `web-${randomId}`;
+}
+
+function resolveRequestIdHeader(headers: Record<string, string>, options: ApiRequestOptions) {
+  const explicitRequestId = options.requestId?.trim();
+  const existingRequestId = Object.entries(headers).find(
+    ([key, value]) => key.toLowerCase() === REQUEST_ID_HEADER && value.trim(),
+  )?.[1];
+  return explicitRequestId || existingRequestId || buildClientRequestId();
+}
+
 function coerceMeta(value: unknown): Partial<ApiMeta> {
   if (!isRecord(value)) {
     return {};
@@ -582,12 +600,14 @@ export async function fetchWithApiAuth(
   const retry = resolveRetryOptions(method, options.retry);
   const authFailurePolicy = resolveAuthFailurePolicy(options);
   const requestSignal = init.signal ?? undefined;
+  const requestId = resolveRequestIdHeader(normalizeHeaders(init.headers), options);
   let attempt = 0;
   let refreshAttempted = false;
 
   for (;;) {
     try {
       let requestHeaders = withAuthorizationHeaders(init.headers, options);
+      requestHeaders[REQUEST_ID_HEADER] = requestId;
       let hasAuthHeader = Boolean(
         requestHeaders.Authorization?.trim() ||
           requestHeaders.authorization?.trim(),
@@ -603,6 +623,7 @@ export async function fetchWithApiAuth(
           // 避免把后端原始 “缺少 Bearer Token” 直接暴露给业务 UI。
           await ensureStoredAccessToken();
           requestHeaders = withAuthorizationHeaders(init.headers, options);
+          requestHeaders[REQUEST_ID_HEADER] = requestId;
           hasAuthHeader = Boolean(
             requestHeaders.Authorization?.trim() ||
               requestHeaders.authorization?.trim(),