Pass TurnContext around instead of sub_id (#5421)

Today `sub_id` is an ID of a single incoming Codex Op submition. We then
associate all events triggered by this operation using the same
`sub_id`.

At the same time we are also creating a TurnContext per submission and
we'd like to start associating some events (item added/item completed)
with an entire turn instead of just the operation that started it.

Using turn context when sending events give us flexibility to change
notification scheme.

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

@@ -11,6 +11,7 @@ use tokio_util::task::AbortOnDropHandle;
 use codex_protocol::models::ResponseInputItem;
 use tokio::sync::oneshot;
 
+use crate::codex::TurnContext;
 use crate::protocol::ReviewDecision;
 use crate::tasks::SessionTask;
 
@@ -53,10 +54,12 @@ pub(crate) struct RunningTask {
     pub(crate) task: Arc<dyn SessionTask>,
     pub(crate) cancellation_token: CancellationToken,
     pub(crate) handle: Arc<AbortOnDropHandle<()>>,
+    pub(crate) turn_context: Arc<TurnContext>,
 }
 
 impl ActiveTurn {
-    pub(crate) fn add_task(&mut self, sub_id: String, task: RunningTask) {
+    pub(crate) fn add_task(&mut self, task: RunningTask) {
+        let sub_id = task.turn_context.sub_id.clone();
         self.tasks.insert(sub_id, task);
     }
 
@@ -65,8 +68,8 @@ impl ActiveTurn {
         self.tasks.is_empty()
     }
 
-    pub(crate) fn drain_tasks(&mut self) -> IndexMap<String, RunningTask> {
-        std::mem::take(&mut self.tasks)
+    pub(crate) fn drain_tasks(&mut self) -> Vec<RunningTask> {
+        self.tasks.drain(..).map(|(_, task)| task).collect()
     }
 }