Restore Guardian risk scores across thread lifecycles (#39038)

## Why

Resumed and forked threads need their persisted Guardian risk state available when routing later approval requests.

## What changed

- Initialize a session's `SecurityRiskScore` from the latest score in its rollout history when no score was supplied explicitly.
- Preserve the inherited score when resuming or forking a thread so low-risk actions can skip redundant Guardian reviews.

## Testing

- Add app-server coverage for inheriting the latest Guardian score when resuming and forking threads.

GitOrigin-RevId: 95a6c803f8dae75516d1da9d66a722379a0a7ef2

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

@@ -26,6 +26,7 @@ use codex_protocol::protocol::MultiAgentVersion;
 use codex_protocol::protocol::ThreadHistoryMode;
 use codex_protocol::protocol::ThreadSource;
 use codex_protocol::protocol::TurnEnvironmentSelections;
+use codex_protocol::security_risk::SecurityRiskScore;
 use codex_skills::SkillError;
 use std::sync::OnceLock;
 use tokio::sync::Semaphore;
@@ -727,6 +728,18 @@ impl Session {
             config.current_time_reminder.as_ref(),
             external_time_provider,
         )?;
+        if thread_extension_init.get::<SecurityRiskScore>().is_none()
+            && let Some(score) = initial_history
+                .get_rollout_items()
+                .iter()
+                .rev()
+                .find_map(|item| match item {
+                    RolloutItem::SecurityRiskScore(score) => Some(score),
+                    _ => None,
+                })
+        {
+            thread_extension_init.insert(score.clone());
+        }
         let selected_capability_roots =
             match thread_extension_init.get::<Vec<SelectedCapabilityRoot>>() {
                 Some(roots) => roots.as_ref().clone(),