Struct ErrorPayload 

pub struct ErrorPayload {
    pub code: i64,
    pub message: String,
    pub details: Option<Value>,
    pub server_version: Option<String>,
    pub client_version: Option<String>,
    pub min_supported: Option<String>,
    pub max_supported: Option<String>,
    pub mcp_server_name: Option<String>,
    pub capability: Option<String>,
    pub extra: Map<String, Value>,
}

A2C-SMCP flat 错误负载 / A2C-SMCP flat error payload

协议 0.2.2 统一错误形态：顶层 code/message，诊断信息置于可选的 details 容器。 禁止嵌套 {"error": {...}} envelope —— 所有 client:* ack 路由的协议级错误 MUST 为本结构。 线格式 / Wire shape: { "code": <int>, "message": <str>, "details"?: <object> }。

details 是诊断容器，Agent MUST NOT 原样透传给最终用户（防信息泄露）。 details is a diagnostic container; the Agent MUST NOT propagate it verbatim to end users.

协议依据 / Protocol: a2c-smcp-protocol error-handling.md（flat ErrorPayload，禁止二次 unwrap）。 Python 参考 / Python reference: a2c_smcp/smcp.py 的 ErrorPayload。

协议 0.2.x 对特定码在顶层平铺分流字段（对齐 Python smcp.py:484 ErrorPayload total=False TypedDict）：

• 4008（协议版本不兼容）→ server_version / client_version / min_supported / max_supported（HS-01 #21 / HS-02 #22；构造见 ErrorPayload::version_mismatch）。
• 4014（MCP Server 未命中）→ mcp_server_name；4015（能力不支持）→ mcp_server_name / capability（SRV-01 #47 / AUTH-01 #23；构造见 ErrorPayload::with_mcp_server_name / ErrorPayload::with_capability）。
• 4016 / 4017 / 4018 的 code-specific 字段下沉到 details 子对象（无顶层平铺新字段）。

未知顶层字段由 ErrorPayload::extra（#[serde(flatten)]）捕获并保留，跨-SDK 往返 不静默丢字段——镜像 Python total=False TypedDict（运行时即 dict）的开放语义，避免旧 Rust SDK 在协议非破坏性新增顶层字段后把它们悄悄抹掉。

Fields

code: i64

错误码（协议 ErrorCode 取值；线格式为裸整数）/ Error code (a protocol ErrorCode value; bare int on the wire)

message: String

人类可读的错误描述 / Human-readable error message

details: Option<Value>

诊断容器（可选；为空时不序列化）/ Diagnostic container (optional; skipped when absent)

server_version: Option<String>

4008 顶层分流：服务端协议版本 / top-level for 4008: server protocol version。

client_version: Option<String>

4008 顶层分流：客户端协议版本 / top-level for 4008: client protocol version。

min_supported: Option<String>

4008 顶层分流：服务端支持的最小版本 / top-level for 4008: min supported。

max_supported: Option<String>

4008 顶层分流：服务端支持的最大版本 / top-level for 4008: max supported。

mcp_server_name: Option<String>

4014 / 4015 顶层分流：未命中 / 缺能力的 MCP Server 名 / top-level for 4014&4015: MCP server name。

capability: Option<String>

4015 顶层分流：缺失的 capability 名（如 "resources"）/ top-level for 4015: missing capability。

extra: Map<String, Value>

未知顶层字段兜底容器：捕获本结构未显式建模的顶层键，跨-SDK 往返不丢字段（见结构体文档）。 为空时不产出任何额外键（空 map flatten 后无输出），故不影响既有 byte 兼容契约。 Catch-all for unmodeled top-level keys so cross-SDK round-trips never silently drop fields.

Implementations

impl ErrorPayload

pub fn new(code: i64, message: impl Into<String>) -> ErrorPayload

创建 flat 错误负载 / Create a flat error payload

pub fn from_error_code( code: ErrorCode, message: impl Into<String>, ) -> ErrorPayload

由协议 ErrorCode 构造 flat 错误负载，消除调用点手工 i64::from(ErrorCode::X.code()) 样板。

产出的 code 必属 is_protocol_error_payload 识别的协议级闭集（编译期由 ErrorCode 保证）， 杜绝误用传输/管理层整数字面量（400 / 401 / 500 / 4101…）落入 client:* ack 致 Agent 端 is_protocol_error_payload 误判为「非协议错误」。

Build a flat payload from a protocol ErrorCode, removing manual i64::from(ErrorCode::X.code()) boilerplate and guaranteeing the wire code is always a protocol-level value recognized by is_protocol_error_payload.

pub fn with_details(self, details: Value) -> ErrorPayload

设置整个 details 诊断容器 / Set the whole details diagnostic container

pub fn with_detail( self, key: impl Into<String>, value: impl Into<Value>, ) -> ErrorPayload

向 details 对象插入单个字段（若 details 非对象则重置为对象） Insert a single field into the details object (reset to an object if it is not one)

pub fn with_mcp_server_name(self, name: impl Into<String>) -> ErrorPayload

顶层平铺 mcp_server_name（4014 / 4015 分流字段）/ Set top-level mcp_server_name (4014/4015).

pub fn with_capability(self, capability: impl Into<String>) -> ErrorPayload

顶层平铺 capability（4015 缺失能力名，如 "resources"）/ Set top-level capability (4015).

pub fn version_mismatch( client: &ProtocolVersion, server: &ProtocolVersion, ) -> ErrorPayload

构造 4008（协议版本不兼容）flat ErrorPayload，顶层平铺 4 个版本分流字段。

min_supported / max_supported 由 server 版本派生：同 MAJOR.MINOR 的整个 PATCH 段 （{maj}.{min}.0 ～ {maj}.{min}.999）。message 固定为 "Protocol version mismatch"。 与 Python middleware _mismatch_body 逐字段对齐。供 HS-01 (#21) 服务端握手中间件复用。

Trait Implementations

impl Clone for ErrorPayload

fn clone(&self) -> ErrorPayload

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ErrorPayload

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for ErrorPayload

fn deserialize<__D>( __deserializer: __D, ) -> Result<ErrorPayload, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for ErrorPayload

fn eq(&self, other: &ErrorPayload) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for ErrorPayload

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for ErrorPayload