support MCP elicitations (#6947)

No support for request schema yet, but we'll at least show the message
and allow accept/decline.

<img width="823" height="551" alt="Screenshot 2025-11-21 at 2 44 05 PM"
src="https://github.com/user-attachments/assets/6fbb892d-ca12-4765-921e-9ac4b217534d"
/>

codex-rs/rmcp-client/src/rmcp_client.rs

@@ -9,6 +9,7 @@ use std::time::Duration;
 use anyhow::Result;
 use anyhow::anyhow;
 use futures::FutureExt;
+use futures::future::BoxFuture;
 use mcp_types::CallToolRequestParams;
 use mcp_types::CallToolResult;
 use mcp_types::InitializeRequestParams;
@@ -21,8 +22,11 @@ use mcp_types::ListToolsRequestParams;
 use mcp_types::ListToolsResult;
 use mcp_types::ReadResourceRequestParams;
 use mcp_types::ReadResourceResult;
+use mcp_types::RequestId;
 use reqwest::header::HeaderMap;
 use rmcp::model::CallToolRequestParam;
+use rmcp::model::CreateElicitationRequestParam;
+use rmcp::model::CreateElicitationResult;
 use rmcp::model::InitializeRequestParam;
 use rmcp::model::PaginatedRequestParam;
 use rmcp::model::ReadResourceRequestParam;
@@ -77,6 +81,14 @@ enum ClientState {
     },
 }
 
+pub type Elicitation = CreateElicitationRequestParam;
+pub type ElicitationResponse = CreateElicitationResult;
+
+/// Interface for sending elicitation requests to the UI and awaiting a response.
+pub type SendElicitation = Box<
+    dyn Fn(RequestId, Elicitation) -> BoxFuture<'static, Result<ElicitationResponse>> + Send + Sync,
+>;
+
 /// MCP client implemented on top of the official `rmcp` SDK.
 /// https://github.com/modelcontextprotocol/rust-sdk
 pub struct RmcpClient {
@@ -200,9 +212,10 @@ impl RmcpClient {
         &self,
         params: InitializeRequestParams,
         timeout: Option<Duration>,
+        send_elicitation: SendElicitation,
     ) -> Result<InitializeResult> {
         let rmcp_params: InitializeRequestParam = convert_to_rmcp(params.clone())?;
-        let client_handler = LoggingClientHandler::new(rmcp_params);
+        let client_handler = LoggingClientHandler::new(rmcp_params, send_elicitation);
 
         let (transport, oauth_persistor) = {
             let mut guard = self.state.lock().await;