Fix canvas transfer timeouts and move images out of snapshots

src/lib/api.ts

@@ -6,7 +6,12 @@ export type Profile = {
   avatar_url?: string | null;
 };
 export class ApiError extends Error {
-  constructor(code: string, readonly status: number, readonly details?: unknown, readonly retryAfter?: string | null) { super(code); this.name = "ApiError"; }
+  readonly status: number;
+  readonly details?: unknown;
+  readonly retryAfter?: string | null;
+  constructor(code: string, status: number, details?: unknown, retryAfter?: string | null) {
+    super(code); this.name = "ApiError"; this.status = status; this.details = details; this.retryAfter = retryAfter;
+  }
 }
 export async function api<T>(
   path: string,
@@ -16,10 +21,20 @@ export async function api<T>(
     ...options,
     headers: { ...(options.body instanceof FormData ? {} : { "Content-Type": "application/json" }), ...options.headers },
   });
-  const body = await res.json().catch(() => null);
+  let body: unknown;
+  if (res.status === 204) body = null;
+  else {
+    try { body = await res.json(); }
+    catch (error) {
+      if (options.signal?.aborted) throw options.signal.reason;
+      const malformed = error instanceof SyntaxError;
+      throw new ApiError(malformed ? "invalid_api_response" : "response_interrupted", res.ok ? 502 : res.status);
+    }
+  }
+  const payload = body as { error?: string | { code?: string }; details?: unknown } | null;
   if (!res.ok) {
-    const code = body?.error?.code || body?.error;
-    throw new ApiError(typeof code === "string" ? code : "request_failed", res.status, body?.details, res.headers.get("retry-after"));
+    const code = typeof payload?.error === "object" ? payload.error?.code : payload?.error;
+    throw new ApiError(typeof code === "string" ? code : "request_failed", res.status, payload?.details, res.headers.get("retry-after"));
   }
   return body as T;
 }
@@ -55,6 +70,11 @@ export const errorText = (error: unknown) => {
     invalid_profile: "请检查显示名称，以及用户名是否为 3–40 位小写字母、数字、下划线或连字符。",
     forbidden: "你没有在此工作空间创建或编辑图谱的权限。",
     invalid_canvas: "画布数据未通过服务端校验，请导出备份后检查节点内容。",
+    response_interrupted: "画布数据传输中断或超时，请重新加载；当前内容未被覆盖。",
+    invalid_api_response: "接口返回了不完整或无法解析的数据，请重新加载。",
+    invalid_asset: "图片格式无法识别，请选择有效的 PNG、JPEG、WebP 或 GIF。",
+    asset_too_large: "图片超出上传限制，请选择小于 20 MiB 的文件。",
+    invalid_asset_response: "图片上传结果无效，画布内容未替换，请重试。",
     invalid_canvas_snapshot: "服务端画布数据格式无效，请重新读取或联系维护者。",
     canvas_schema_upgrade_required: "这张画布已升级，请刷新以加载新版客户端。",
     undo_receipt_expired: "撤销记录已过期，当前内容已保留。",