feat(core): store turn_id on ResponseItem metadata (#28360)

## Description

This PR is a followup to https://github.com/openai/codex/pull/28355 and
starts assigning `internal_chat_message_metadata_passthrough.turn_id` to
durable Responses API items created during a turn.

The goal is that those items keep the `turn_id` that introduced them
when Codex resends stateless HTTP context, reconstructs history for
resume/fork paths, or reuses websocket response state.

## What changed

- Set `internal_chat_message_metadata_passthrough.turn_id` when missing
as response items enter durable history, initial/replacement history,
inter-agent communication history, and local compaction summaries.
- Preserve existing item turn IDs instead of overwriting them during
persistence, resume reconstruction, compaction, forked history, and
websocket incremental reuse.
- Keep `compaction_trigger` fieldless because it is a request control,
not a durable response item.
- Update focused history/request assertions and fixtures for stateless
requests, websocket incrementals, compaction, thread injection, prompt
debug, and related CI coverage.

codex-rs/core/src/compact.rs

@@ -302,6 +302,11 @@ async fn run_compact_task_inner_impl(
     let user_messages = collect_user_messages(history_items);
 
     let mut new_history = build_compacted_history(Vec::new(), &user_messages, &summary_text);
+    if let Some(summary_item) = new_history.last_mut() {
+        // This replacement history skips `record_conversation_items`; only the appended summary
+        // belongs to this compaction turn.
+        summary_item.set_turn_id_if_missing(&turn_context.sub_id);
+    }
     let (window_number, window_ids) = sess.advance_auto_compact_window().await;
 
     if matches!(