Persist security risk scores in rollout history (#38363)

## What changed

- Add a `SecurityRiskScore` rollout item containing a category and numeric score.
- Persist the item in both thread history modes while excluding it from model context, user-visible thread history, search text, forks, and reconstructed conversation history.
- Re-export the score type from the extension API.

## Testing

- Cover serialization, persistence and loading, thread history projection, session reconstruction, append planning, and memory filtering.

GitOrigin-RevId: 1926fe366aeaa75052708a6da589f45a38eefb52

codex-rs/memories/write/src/phase1.rs

@@ -417,6 +417,7 @@ mod job {
                 | RolloutItem::Compacted(_)
                 | RolloutItem::TurnContext(_)
                 | RolloutItem::WorldState(_)
+                | RolloutItem::SecurityRiskScore(_)
                 | RolloutItem::EventMsg(_) => None,
             })
             .collect::<Vec<_>>();
@@ -672,6 +673,7 @@ mod tests {
     use super::*;
     use codex_protocol::AgentPath;
     use codex_protocol::protocol::InterAgentCommunication;
+    use codex_protocol::security_risk::SecurityRiskScore;
     use pretty_assertions::assert_eq;
 
     #[test]
@@ -722,6 +724,10 @@ mod tests {
         let serialized = job::serialize_filtered_rollout_response_items(&[
             RolloutItem::ResponseItem(mixed_contextual_message.into()),
             RolloutItem::ResponseItem(skill_message.into()),
+            RolloutItem::SecurityRiskScore(SecurityRiskScore {
+                category: "action_risk".to_string(),
+                score: 0.92,
+            }),
             RolloutItem::ResponseItem(subagent_message.clone().into()),
         ])
         .expect("serialize");