Persist agent messages as response items (#29829)

## Why

Inter-agent messages are recorded in live history as
`ResponseItem::AgentMessage`, but rollouts stored
`InterAgentCommunication` and rebuilt the response item during resume.
This made the rollout differ from the actual Responses history.

## What changed

- store the prepared `agent_message` response item directly
- keep `trigger_turn` in a small local metadata record for fork
truncation
- keep reading older `inter_agent_communication` rollout items

codex-rs/state/src/extract.rs

@@ -22,7 +22,8 @@ pub fn apply_rollout_item(
         RolloutItem::TurnContext(turn_ctx) => apply_turn_context(metadata, turn_ctx),
         RolloutItem::EventMsg(event) => apply_event_msg(metadata, event),
         RolloutItem::ResponseItem(item) => apply_response_item(metadata, item),
-        RolloutItem::InterAgentCommunication(_) => {}
+        RolloutItem::InterAgentCommunication(_)
+        | RolloutItem::InterAgentCommunicationMetadata { .. } => {}
         RolloutItem::Compacted(_) => {}
     }
     if metadata.model_provider.is_empty() {
@@ -40,6 +41,7 @@ pub fn rollout_item_affects_thread_metadata(item: &RolloutItem) -> bool {
         RolloutItem::EventMsg(_)
         | RolloutItem::ResponseItem(_)
         | RolloutItem::InterAgentCommunication(_)
+        | RolloutItem::InterAgentCommunicationMetadata { .. }
         | RolloutItem::Compacted(_) => false,
     }
 }

codex-rs/state/src/runtime/threads.rs

@@ -1163,6 +1163,7 @@ pub(super) fn extract_memory_mode(items: &[RolloutItem]) -> Option<String> {
         RolloutItem::SessionMeta(meta_line) => meta_line.meta.memory_mode.clone(),
         RolloutItem::ResponseItem(_)
         | RolloutItem::InterAgentCommunication(_)
+        | RolloutItem::InterAgentCommunicationMetadata { .. }
         | RolloutItem::Compacted(_)
         | RolloutItem::TurnContext(_)
         | RolloutItem::EventMsg(_) => None,