Add a getUserAgent MCP method (#3320)

This will allow the extension to pass this user agent + a suffix for its
requests

codex-rs/mcp-server/tests/common/mcp_process.rs

@@ -247,6 +247,11 @@ impl McpProcess {
         self.send_request("getUserSavedConfig", None).await
     }
 
+    /// Send a `getUserAgent` JSON-RPC request.
+    pub async fn send_get_user_agent_request(&mut self) -> anyhow::Result<i64> {
+        self.send_request("getUserAgent", None).await
+    }
+
     /// Send a `listConversations` JSON-RPC request.
     pub async fn send_list_conversations_request(
         &mut self,

codex-rs/mcp-server/tests/suite/mod.rs

@@ -8,3 +8,4 @@ mod interrupt;
 mod list_resume;
 mod login;
 mod send_message;
+mod user_agent;

codex-rs/mcp-server/tests/suite/user_agent.rs

@@ -0,0 +1,45 @@
+use codex_core::default_client::DEFAULT_ORIGINATOR;
+use codex_core::default_client::get_codex_user_agent;
+use codex_protocol::mcp_protocol::GetUserAgentResponse;
+use mcp_test_support::McpProcess;
+use mcp_test_support::to_response;
+use mcp_types::JSONRPCResponse;
+use mcp_types::RequestId;
+use pretty_assertions::assert_eq;
+use tempfile::TempDir;
+use tokio::time::timeout;
+
+const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn get_user_agent_returns_current_codex_user_agent() {
+    let codex_home = TempDir::new().unwrap_or_else(|err| panic!("create tempdir: {err}"));
+
+    let mut mcp = McpProcess::new(codex_home.path())
+        .await
+        .expect("spawn mcp process");
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize())
+        .await
+        .expect("initialize timeout")
+        .expect("initialize request");
+
+    let request_id = mcp
+        .send_get_user_agent_request()
+        .await
+        .expect("send getUserAgent");
+    let response: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id)),
+    )
+    .await
+    .expect("getUserAgent timeout")
+    .expect("getUserAgent response");
+
+    let received: GetUserAgentResponse =
+        to_response(response).expect("deserialize getUserAgent response");
+    let expected = GetUserAgentResponse {
+        user_agent: get_codex_user_agent(Some(DEFAULT_ORIGINATOR)),
+    };
+
+    assert_eq!(received, expected);
+}