private isPlainObject(value: unknown): value is Record<string, unknown> {
 if (typeof value !== 'object' || value === null) return false
 const proto = Object.getPrototypeOf(value)
 return proto === null || proto === Object.prototype
 }
 private normalizeHeaders(headers: unknown): Record<string, string> | undefined {
 if (headers == null) return undefined
 if (!this.isPlainObject(headers)) {
 throw new Error('headers 必须是对象')
 }
 const normalized: Record<string, string> = {}
 for (const [key, value] of Object.entries(headers)) {
 if (value !== null && value !== undefined) {
 normalized[key] = String(value)
 }
 }
 return Object.keys(normalized).length > 0 ? normalized : undefined
 }
 private normalizeExtraBody(extraBody: unknown): Record<string, unknown> | undefined {
 if (extraBody == null) return undefined
 if (!this.isPlainObject(extraBody)) {
 throw new Error('extraBody 必须是对象')
 }
 const normalized = { ...extraBody }
 for (const key of RESERVED_EXTRA_BODY_KEYS) {
 delete normalized[key]
 }
 return Object.keys(normalized).length > 0 ? normalized : undefined
 }