[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/turn.rs

@@ -1877,6 +1877,12 @@ async fn try_run_sampling_request(
         auth_mode = sess.services.auth_manager.auth_mode(),
         features = sess.features.enabled_features(),
     );
+    let inference_trace = sess.services.rollout_trace.inference_trace_context(
+        sess.conversation_id,
+        turn_context.sub_id.as_str(),
+        turn_context.model_info.slug.as_str(),
+        turn_context.provider.info().name.as_str(),
+    );
     let mut stream = client_session
         .stream(
             prompt,
@@ -1886,6 +1892,7 @@ async fn try_run_sampling_request(
             turn_context.reasoning_summary,
             turn_context.config.service_tier,
             turn_metadata_header,
+            &inference_trace,
         )
         .instrument(trace_span!("stream_request"))
         .or_cancel(&cancellation_token)