Introduce rollout items (#3380)

This PR introduces Rollout items. This enable us to rollout eventmsgs
and session meta.

This is mostly #3214 with rebase on main

codex-rs/mcp-server/tests/suite/list_resume.rs

@@ -156,14 +156,45 @@ fn create_fake_rollout(codex_home: &Path, filename_ts: &str, meta_rfc3339: &str,
 
     let file_path = dir.join(format!("rollout-{filename_ts}-{uuid}.jsonl"));
     let mut lines = Vec::new();
-    // Meta line with timestamp
-    lines.push(json!({"timestamp": meta_rfc3339, "id": uuid}).to_string());
-    // Minimal user message entry as a persisted response item
+    // Meta line with timestamp (flattened meta in payload for new schema)
     lines.push(
         json!({
-            "type":"message",
-            "role":"user",
-            "content":[{"type":"input_text","text": preview}]
+            "timestamp": meta_rfc3339,
+            "type": "session_meta",
+            "payload": {
+                "id": uuid,
+                "timestamp": meta_rfc3339,
+                "cwd": "/",
+                "originator": "codex",
+                "cli_version": "0.0.0",
+                "instructions": null
+            }
+        })
+        .to_string(),
+    );
+    // Minimal user message entry as a persisted response item (with envelope timestamp)
+    lines.push(
+        json!({
+            "timestamp": meta_rfc3339,
+            "type":"response_item",
+            "payload": {
+                "type":"message",
+                "role":"user",
+                "content":[{"type":"input_text","text": preview}]
+            }
+        })
+        .to_string(),
+    );
+    // Add a matching user message event line to satisfy filters
+    lines.push(
+        json!({
+            "timestamp": meta_rfc3339,
+            "type":"event_msg",
+            "payload": {
+                "type":"user_message",
+                "message": preview,
+                "kind": "plain"
+            }
         })
         .to_string(),
     );