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/tools/router_tests.rs

@@ -345,6 +345,8 @@ async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow
     session
         .record_conversation_items(&turn, std::slice::from_ref(&history_item))
         .await;
+    let mut expected_history_item = history_item.clone();
+    expected_history_item.set_turn_id_if_missing(&turn.sub_id);
 
     let router = ToolRouter::from_turn_context(
         &turn,
@@ -404,7 +406,7 @@ async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow
                 json!({
                     "arguments": { "message": "hello" },
                     "callId": "call-extension",
-                    "conversationHistory": [history_item],
+                    "conversationHistory": [expected_history_item],
                     "ok": true,
                 })
             );