Move Guardian reporting and denial accounting into the extension (#44544)

## What changed

- Move assessment event construction, metrics, and analytics tracking into `codex-guardian-reviewer` through `ReviewReport`.
- Store denial accounting in thread extension data through `ReviewDenials`, with core retaining turn interruption and lifecycle cleanup.
- Move failed-review record selection and bounded serialization into the extension, with core supplying captured review context.

## Testing

Add coverage that denial accounting clears on turn completion and interruption. Move the oversized-record test into the extension and exercise the new API.

GitOrigin-RevId: 6e5b3d9d4128b356f99b1d0e74a68111e40261ab

codex-rs/core/src/session/tests/guardian_tests.rs

@@ -1324,3 +1324,48 @@ async fn guardian_subagent_does_not_inherit_parent_exec_policy_rules() {
     );
     drop(io);
 }
+
+#[test_case(TerminalEventKind::TurnComplete; "completion")]
+#[test_case(TerminalEventKind::TurnAborted; "interruption")]
+#[tokio::test]
+async fn terminal_turn_clears_extension_owned_denials(terminal: TerminalEventKind) {
+    let (session, turn, events) = make_session_and_context_with_rx().await;
+    let finish = Arc::new(tokio::sync::Notify::new());
+    session
+        .spawn_task(
+            Arc::clone(&turn),
+            Vec::new(),
+            HeldStepTask {
+                kind: TaskKind::Regular,
+                finish: Arc::clone(&finish),
+            },
+        )
+        .await;
+    let denials =
+        codex_guardian_reviewer::ReviewDenials::for_thread(&session.services.thread_extension_data);
+    for _ in 0..2 {
+        assert_eq!(
+            denials.record_denial(&turn.sub_id, turn.model_info()).await,
+            None
+        );
+    }
+    match terminal {
+        TerminalEventKind::TurnComplete => finish.notify_one(),
+        TerminalEventKind::TurnAborted => {
+            session.abort_all_tasks(TurnAbortReason::Interrupted).await
+        }
+    }
+    recv_terminal_event(&events, terminal).await;
+    // Delivery precedes accounting cleanup. Wait for the runtime to finish the turn.
+    timeout(Duration::from_secs(/*secs*/ 5), async {
+        while session.active_turn.lock().await.is_some() {
+            tokio::task::yield_now().await;
+        }
+    })
+    .await
+    .expect("turn becomes idle");
+    assert_eq!(
+        denials.record_denial(&turn.sub_id, turn.model_info()).await,
+        None
+    );
+}