Persist multi-agent runtime metadata (#25721)

Stack split from #25708. Original PR intentionally left open. This
second PR persists multi-agent runtime metadata through thread creation,
rollout recording, and thread storage.

codex-rs/app-server/tests/suite/conversation_summary.rs

@@ -128,6 +128,7 @@ async fn get_conversation_summary_by_thread_id_reads_pathless_store_thread() ->
             thread_source: None,
             base_instructions: BaseInstructions::default(),
             dynamic_tools: Vec::new(),
+            multi_agent_version: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
                 model_provider: "test-provider".to_string(),

codex-rs/app-server/tests/suite/v2/thread_read.rs

@@ -1362,6 +1362,7 @@ async fn seed_pathless_store_thread(
             thread_source: None,
             base_instructions: BaseInstructions::default(),
             dynamic_tools: Vec::new(),
+            multi_agent_version: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
                 model_provider: "test-provider".to_string(),

codex-rs/app-server/tests/suite/v2/thread_unarchive.rs

@@ -215,6 +215,7 @@ async fn thread_unarchive_preserves_pathless_store_metadata() -> Result<()> {
             thread_source: None,
             base_instructions: BaseInstructions::default(),
             dynamic_tools: Vec::new(),
+            multi_agent_version: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
                 model_provider: "test-provider".to_string(),