feat: async ghost commit (#5618)

codex-rs/protocol/src/models.rs

@@ -116,6 +116,12 @@ pub enum ResponseItem {
         status: Option<String>,
         action: WebSearchAction,
     },
+    // Generated by the harness but considered exactly as a model response.
+    GhostSnapshot {
+        commit_id: String,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        parent: Option<String>,
+    },
     #[serde(other)]
     Other,
 }