feat: remote compaction (#6795)

Co-authored-by: pakrym-oai <pakrym@openai.com>

codex-rs/protocol/src/protocol.rs

@@ -1126,6 +1126,8 @@ pub enum RolloutItem {
 #[derive(Serialize, Deserialize, Clone, Debug, JsonSchema, TS)]
 pub struct CompactedItem {
     pub message: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub replacement_history: Option<Vec<ResponseItem>>,
 }
 
 impl From<CompactedItem> for ResponseItem {