Add ItemStarted/ItemCompleted events for UserInputItem (#5306)

Adds a new ItemStarted event and delivers UserMessage as the first item
type (more to come).


Renames `InputItem` to `UserInput` considering we're using the `Item`
suffix for actual items.

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -18,11 +18,11 @@ use codex_core::protocol::ApplyPatchApprovalRequestEvent;
 use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::ExecApprovalRequestEvent;
-use codex_core::protocol::InputItem;
 use codex_core::protocol::Op;
 use codex_core::protocol::Submission;
 use codex_core::protocol::TaskCompleteEvent;
 use codex_protocol::ConversationId;
+use codex_protocol::user_input::UserInput;
 use mcp_types::CallToolResult;
 use mcp_types::ContentBlock;
 use mcp_types::RequestId;
@@ -91,7 +91,7 @@ pub async fn run_codex_tool_session(
     let submission = Submission {
         id: sub_id.clone(),
         op: Op::UserInput {
-            items: vec![InputItem::Text {
+            items: vec![UserInput::Text {
                 text: initial_prompt.clone(),
             }],
         },
@@ -127,7 +127,7 @@ pub async fn run_codex_tool_session_reply(
         .insert(request_id.clone(), conversation_id);
     if let Err(e) = conversation
         .submit(Op::UserInput {
-            items: vec![InputItem::Text { text: prompt }],
+            items: vec![UserInput::Text { text: prompt }],
         })
         .await
     {
@@ -284,6 +284,8 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::ShutdownComplete
                     | EventMsg::ViewImageToolCall(_)
                     | EventMsg::EnteredReviewMode(_)
+                    | EventMsg::ItemStarted(_)
+                    | EventMsg::ItemCompleted(_)
                     | EventMsg::ExitedReviewMode(_) => {
                         // For now, we do not do anything extra for these
                         // events. Note that