[rollout_trace] Record core session rollout traces (#18877)

## Summary

Wires rollout trace recording into `codex-core` session and turn
execution. This records the core model request/response, compaction, and
session lifecycle boundaries needed for replay without yet tracing every
nested runtime/tool boundary.

## Stack

This is PR 2/5 in the rollout trace stack.

- [#18876](https://github.com/openai/codex/pull/18876): Add rollout
trace crate
- [#18877](https://github.com/openai/codex/pull/18877): Record core
session rollout traces
- [#18878](https://github.com/openai/codex/pull/18878): Trace tool and
code-mode boundaries
- [#18879](https://github.com/openai/codex/pull/18879): Trace sessions
and multi-agent edges
- [#18880](https://github.com/openai/codex/pull/18880): Add debug trace
reduction command

## Review Notes

This layer is the first live integration point. The important review
question is whether trace recording is isolated from normal session
behavior: trace failures should not become user-visible execution
failures, and recording should preserve the existing turn/session
lifecycle semantics.

The PR depends on the reducer/data model from the first stack entry and
only introduces the core recorder surface that later PRs use for richer
runtime and relationship events.

codex-rs/core/src/session/tests.rs

@@ -2959,6 +2959,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_zsh_path() {
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         /*analytics_events_client*/ None,
+        RolloutTraceRecorder::disabled(),
     )
     .await;
 
@@ -3081,6 +3082,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
             ..HooksConfig::default()
         }),
         rollout: Mutex::new(None),
+        rollout_trace: RolloutTraceRecorder::disabled(),
         user_shell: Arc::new(default_user_shell()),
         shell_snapshot_tx: watch::channel(None).0,
         show_raw_agent_reasoning: config.show_raw_agent_reasoning,
@@ -3274,6 +3276,7 @@ async fn make_session_with_config_and_rx(
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         /*analytics_events_client*/ None,
+        RolloutTraceRecorder::disabled(),
     )
     .await?;
 
@@ -4299,6 +4302,7 @@ pub(crate) async fn make_session_and_context_with_dynamic_tools_and_rx(
             ..HooksConfig::default()
         }),
         rollout: Mutex::new(None),
+        rollout_trace: RolloutTraceRecorder::disabled(),
         user_shell: Arc::new(default_user_shell()),
         shell_snapshot_tx: watch::channel(None).0,
         show_raw_agent_reasoning: config.show_raw_agent_reasoning,