Preserve model-facing ID allocations in saved history (#60771)

## Why

Restoring model-facing ID sequences requires allocation ordinals alongside the rendered IDs. Responses API payloads still require string IDs.

## What changed

- Add allocation metadata to `ResponseItemId` while keeping equality, hashing, and ordering based on the rendered ID.
- Preserve optional `id_allocation` metadata in rollout items, inter-agent messages, compaction replacement history, and Guardian checkpoints. Continue accepting legacy string IDs.
- Support structured context-window allocations alongside UUIDv7 strings, validate the `window` salt on restoration, and keep request metadata IDs as strings.

## Testing

Add tests for allocation round trips, legacy ID compatibility, string-only raw response item IDs, and context-window allocation validation.

GitOrigin-RevId: ce1fd964bde9a4e7c527432be99aea87ada30169

codex-rs/protocol/src/protocol.rs

@@ -61,6 +61,7 @@ use crate::plan_tool::UpdatePlanArgs;
 use crate::request_permissions::RequestPermissionsEvent;
 use crate::request_permissions::RequestPermissionsResponse;
 use crate::request_user_input::RequestUserInputResponse;
+use crate::response_item_id::OptionalWireItemId;
 use crate::turn_input::CyberAccessProgram;
 use crate::turn_input::SuspendTurnOutcome;
 use crate::turn_input::TurnInputMode;
@@ -994,7 +995,8 @@ impl FromStr for ThreadHistoryMode {
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, JsonSchema, TS)]
 pub struct InterAgentCommunication {
     #[serde(default, skip_serializing_if = "Option::is_none")]
-    #[ts(optional)]
+    #[serde(with = "OptionalWireItemId")]
+    #[ts(optional, as = "Option<ResponseItemId>")]
     pub id: Option<ResponseItemId>,
     pub author: AgentPath,
     pub recipient: AgentPath,
@@ -3450,7 +3452,7 @@ pub enum MultiAgentVersion {
 
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq, JsonSchema)]
 pub struct SessionContextWindow {
-    /// UUIDv7 identity of this context window.
+    /// Persisted model-facing window identity.
     pub window_id: crate::ContextWindowId,
 }