[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/tests/suite/client.rs

@@ -914,6 +914,7 @@ async fn send_provider_auth_request(server: &MockServer, auth: ModelProviderAuth
             summary.unwrap_or(ReasoningSummary::Auto),
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("responses stream to start");
@@ -2280,6 +2281,7 @@ async fn azure_responses_request_includes_store_and_reasoning_ids() {
             summary.unwrap_or(ReasoningSummary::Auto),
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("responses stream to start");

codex-rs/core/tests/suite/client_websockets.rs

@@ -390,6 +390,7 @@ async fn responses_websocket_preconnect_is_reused_even_with_header_changes() {
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -440,6 +441,7 @@ async fn responses_websocket_request_prewarm_is_reused_even_with_header_changes(
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -842,6 +844,7 @@ async fn responses_websocket_emits_reasoning_included_event() {
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -915,6 +918,7 @@ async fn responses_websocket_emits_rate_limit_events() {
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -1553,6 +1557,7 @@ async fn responses_websocket_v2_after_error_uses_full_create_without_previous_re
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -1640,6 +1645,7 @@ async fn responses_websocket_v2_surfaces_terminal_error_without_close_handshake(
             harness.summary,
             /*service_tier*/ None,
             /*turn_metadata_header*/ None,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");
@@ -1903,6 +1909,7 @@ async fn stream_until_complete_with_request_metadata(
             harness.summary,
             service_tier,
             turn_metadata_header,
+            &codex_rollout_trace::InferenceTraceContext::disabled(),
         )
         .await
         .expect("websocket stream failed");