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/rollout/src/policy.rs

@@ -6,7 +6,8 @@ use codex_protocol::models::ResponseItem;
 pub fn is_persisted_rollout_item(item: &RolloutItem) -> bool {
     match item {
         RolloutItem::ResponseItem(item) => should_persist_response_item(item),
-        RolloutItem::InterAgentCommunication(_) => true,
+        RolloutItem::InterAgentCommunication(_)
+        | RolloutItem::InterAgentCommunicationMetadata { .. } => true,
         RolloutItem::EventMsg(ev) => should_persist_event_msg(ev),
         // Persist Codex executive markers so we can analyze flows (e.g., compaction, API turns).
         RolloutItem::Compacted(_) | RolloutItem::TurnContext(_) | RolloutItem::SessionMeta(_) => {
@@ -55,7 +56,8 @@ pub fn should_persist_response_item(item: &ResponseItem) -> bool {
 pub fn should_persist_response_item_for_memories(item: &ResponseItem) -> bool {
     match item {
         ResponseItem::Message { role, .. } => role != "developer",
-        ResponseItem::LocalShellCall { .. }
+        ResponseItem::AgentMessage { .. }
+        | ResponseItem::LocalShellCall { .. }
         | ResponseItem::FunctionCall { .. }
         | ResponseItem::ToolSearchCall { .. }
         | ResponseItem::FunctionCallOutput { .. }
@@ -64,7 +66,6 @@ pub fn should_persist_response_item_for_memories(item: &ResponseItem) -> bool {
         | ResponseItem::CustomToolCallOutput { .. }
         | ResponseItem::WebSearchCall { .. } => true,
         ResponseItem::AdditionalTools { .. }
-        | ResponseItem::AgentMessage { .. }
         | ResponseItem::Reasoning { .. }
         | ResponseItem::ImageGenerationCall { .. }
         | ResponseItem::Compaction { .. }