Wire turn item contributors into stream output (#22494)

## Summary
- run registered TurnItemContributor hooks for parsed stream output
items
- plumb the active turn extension store into stream item handling
- preserve existing memory citation parsing as fallback after
contributors run

## Tests
- cargo test -p codex-core stream_events_utils -- --nocapture
- just fmt
- just fix -p codex-core
- git diff --check

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

@@ -8,6 +8,7 @@ use std::sync::Arc;
 use std::time::Duration;
 use std::time::Instant;
 
+use codex_extension_api::ExtensionData;
 use futures::future::BoxFuture;
 use tokio::select;
 use tokio::sync::Notify;
@@ -153,17 +154,25 @@ fn bool_tag(value: bool) -> &'static str {
 #[derive(Clone)]
 pub(crate) struct SessionTaskContext {
     session: Arc<Session>,
+    turn_extension_data: Arc<ExtensionData>,
 }
 
 impl SessionTaskContext {
-    pub(crate) fn new(session: Arc<Session>) -> Self {
-        Self { session }
+    pub(crate) fn new(session: Arc<Session>, turn_extension_data: Arc<ExtensionData>) -> Self {
+        Self {
+            session,
+            turn_extension_data,
+        }
     }
 
     pub(crate) fn clone_session(&self) -> Arc<Session> {
         Arc::clone(&self.session)
     }
 
+    pub(crate) fn turn_extension_data(&self) -> Arc<ExtensionData> {
+        Arc::clone(&self.turn_extension_data)
+    }
+
     pub(crate) fn auth_manager(&self) -> Arc<AuthManager> {
         Arc::clone(&self.session.services.auth_manager)
     }
@@ -362,7 +371,10 @@ impl Session {
         let turn = active.get_or_insert_with(ActiveTurn::default);
         debug_assert!(turn.tasks.is_empty());
         let done_clone = Arc::clone(&done);
-        let session_ctx = Arc::new(SessionTaskContext::new(Arc::clone(self)));
+        let session_ctx = Arc::new(SessionTaskContext::new(
+            Arc::clone(self),
+            Arc::clone(&turn_extension_data),
+        ));
         let ctx = Arc::clone(&turn_context);
         let task_for_run = Arc::clone(&task);
         let task_cancellation_token = cancellation_token.child_token();
@@ -829,7 +841,10 @@ impl Session {
 
         task.handle.abort();
 
-        let session_ctx = Arc::new(SessionTaskContext::new(Arc::clone(self)));
+        let session_ctx = Arc::new(SessionTaskContext::new(
+            Arc::clone(self),
+            Arc::clone(&task.turn_extension_data),
+        ));
         session_task
             .abort(session_ctx, Arc::clone(&task.turn_context))
             .await;

codex-rs/core/src/tasks/regular.rs

@@ -45,6 +45,7 @@ impl SessionTask for RegularTask {
         cancellation_token: CancellationToken,
     ) -> Option<String> {
         let sess = session.clone_session();
+        let turn_extension_data = session.turn_extension_data();
         let run_turn_span = trace_span!("run_turn");
         // Regular turns emit `TurnStarted` inline so first-turn lifecycle does
         // not wait on startup prewarm resolution.
@@ -72,6 +73,7 @@ impl SessionTask for RegularTask {
             let last_agent_message = run_turn(
                 Arc::clone(&sess),
                 Arc::clone(&ctx),
+                Arc::clone(&turn_extension_data),
                 next_input,
                 prewarmed_client_session.take(),
                 cancellation_token.child_token(),