Set a user agent suffix when used as a mcp server (#3395)

This automatically adds a user agent suffix whenever the CLI is used as
a MCP server

codex-rs/mcp-types/src/lib.rs

@@ -482,13 +482,23 @@ pub struct ImageContent {
 
 /// Describes the name and version of an MCP implementation, with an optional title for UI representation.
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize, TS)]
-pub struct Implementation {
+pub struct McpClientInfo {
     pub name: String,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub title: Option<String>,
     pub version: String,
 }
 
+/// Describes the name and version of an MCP implementation, with an optional title for UI representation.
+#[derive(Debug, Clone, PartialEq, Deserialize, Serialize, TS)]
+pub struct McpServerInfo {
+    pub name: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub title: Option<String>,
+    pub version: String,
+    pub user_agent: String,
+}
+
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize, TS)]
 pub enum InitializeRequest {}
 
@@ -502,7 +512,7 @@ impl ModelContextProtocolRequest for InitializeRequest {
 pub struct InitializeRequestParams {
     pub capabilities: ClientCapabilities,
     #[serde(rename = "clientInfo")]
-    pub client_info: Implementation,
+    pub client_info: McpClientInfo,
     #[serde(rename = "protocolVersion")]
     pub protocol_version: String,
 }
@@ -516,7 +526,7 @@ pub struct InitializeResult {
     #[serde(rename = "protocolVersion")]
     pub protocol_version: String,
     #[serde(rename = "serverInfo")]
-    pub server_info: Implementation,
+    pub server_info: McpServerInfo,
 }
 
 impl From<InitializeResult> for serde_json::Value {

codex-rs/mcp-types/tests/suite/initialize.rs

@@ -1,10 +1,10 @@
 use mcp_types::ClientCapabilities;
 use mcp_types::ClientRequest;
-use mcp_types::Implementation;
 use mcp_types::InitializeRequestParams;
 use mcp_types::JSONRPC_VERSION;
 use mcp_types::JSONRPCMessage;
 use mcp_types::JSONRPCRequest;
+use mcp_types::McpClientInfo;
 use mcp_types::RequestId;
 use serde_json::json;
 
@@ -58,7 +58,7 @@ fn deserialize_initialize_request() {
                 sampling: None,
                 elicitation: None,
             },
-            client_info: Implementation {
+            client_info: McpClientInfo {
                 name: "acme-client".into(),
                 title: Some("Acme".to_string()),
                 version: "1.2.3".into(),