Add new thread items and rewire event parsing to use them (#5418)

1. Adds AgentMessage,  Reasoning,  WebSearch items.
2. Switches the ResponseItem parsing to use new items and then also emit
3. Removes user-item kind and filters out "special" (environment) user
items when returning to clients.

codex-rs/core/src/state/item_collector.rs

@@ -1,68 +0,0 @@
-use async_channel::Sender;
-use codex_protocol::ConversationId;
-use codex_protocol::items::TurnItem;
-use codex_protocol::protocol::Event;
-use codex_protocol::protocol::EventMsg;
-use codex_protocol::protocol::ItemCompletedEvent;
-use codex_protocol::protocol::ItemStartedEvent;
-use tracing::error;
-
-#[derive(Debug)]
-pub(crate) struct ItemCollector {
-    thread_id: ConversationId,
-    turn_id: String,
-    tx_event: Sender<Event>,
-}
-
-impl ItemCollector {
-    pub fn new(
-        tx_event: Sender<Event>,
-        thread_id: ConversationId,
-        turn_id: String,
-    ) -> ItemCollector {
-        ItemCollector {
-            tx_event,
-            thread_id,
-            turn_id,
-        }
-    }
-
-    pub async fn started(&self, item: TurnItem) {
-        let err = self
-            .tx_event
-            .send(Event {
-                id: self.turn_id.clone(),
-                msg: EventMsg::ItemStarted(ItemStartedEvent {
-                    thread_id: self.thread_id,
-                    turn_id: self.turn_id.clone(),
-                    item,
-                }),
-            })
-            .await;
-        if let Err(e) = err {
-            error!("failed to send item started event: {e}");
-        }
-    }
-
-    pub async fn completed(&self, item: TurnItem) {
-        let err = self
-            .tx_event
-            .send(Event {
-                id: self.turn_id.clone(),
-                msg: EventMsg::ItemCompleted(ItemCompletedEvent {
-                    thread_id: self.thread_id,
-                    turn_id: self.turn_id.clone(),
-                    item,
-                }),
-            })
-            .await;
-        if let Err(e) = err {
-            error!("failed to send item completed event: {e}");
-        }
-    }
-
-    pub async fn started_completed(&self, item: TurnItem) {
-        self.started(item.clone()).await;
-        self.completed(item).await;
-    }
-}

codex-rs/core/src/state/mod.rs

@@ -1,9 +1,7 @@
-mod item_collector;
 mod service;
 mod session;
 mod turn;
 
-pub(crate) use item_collector::ItemCollector;
 pub(crate) use service::SessionServices;
 pub(crate) use session::SessionState;
 pub(crate) use turn::ActiveTurn;