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/tests/resources.rs

@@ -2,8 +2,11 @@ use std::ffi::OsString;
 use std::path::PathBuf;
 use std::time::Duration;
 
+use codex_rmcp_client::ElicitationAction;
+use codex_rmcp_client::ElicitationResponse;
 use codex_rmcp_client::RmcpClient;
 use escargot::CargoBuild;
+use futures::FutureExt as _;
 use mcp_types::ClientCapabilities;
 use mcp_types::Implementation;
 use mcp_types::InitializeRequestParams;
@@ -55,7 +58,19 @@ async fn rmcp_client_can_list_and_read_resources() -> anyhow::Result<()> {
     .await?;
 
     client
-        .initialize(init_params(), Some(Duration::from_secs(5)))
+        .initialize(
+            init_params(),
+            Some(Duration::from_secs(5)),
+            Box::new(|_, _| {
+                async {
+                    Ok(ElicitationResponse {
+                        action: ElicitationAction::Accept,
+                        content: Some(json!({})),
+                    })
+                }
+                .boxed()
+            }),
+        )
         .await?;
 
     let list = client