Record realtime close marker on replacement (#13058)

## Summary
- record a realtime close developer message when a new realtime session
replaces an active one
- assert the replacement marker through the mocked responses request
path

---------

Co-authored-by: Codex <noreply@openai.com>
Co-authored-by: Charles Cunningham <ccunningham@openai.com>

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

@@ -628,6 +628,7 @@ fn append_rollout_turn_context(path: &Path, timestamp: &str, model: &str) -> std
             model: model.to_string(),
             personality: None,
             collaboration_mode: None,
+            realtime_active: Some(false),
             effort: None,
             summary: ReasoningSummary::Auto,
             user_instructions: None,