Add collaboration_mode to TurnContextItem (#9583)

## Summary
- add optional `collaboration_mode` to `TurnContextItem` in rollouts
- persist the current collaboration mode when recording turn context
(sampling + compaction)

## Rationale
We already persist turn context data for resume logic. Capturing
collaboration mode in the rollout gives us the mode context for each
turn, enabling follow‑up work to diff mode instructions correctly on
resume.

## Changes
- protocol: add optional `collaboration_mode` field to `TurnContextItem`
- core: persist collaboration mode alongside other turn context settings
in rollouts

codex-rs/core/src/compact.rs

@@ -84,11 +84,17 @@ async fn run_compact_task_inner(
     let max_retries = turn_context.client.get_provider().stream_max_retries();
     let mut retries = 0;
 
+    // TODO: If we need to guarantee the persisted mode always matches the prompt used for this
+    // turn, capture it in TurnContext at creation time. Using SessionConfiguration here avoids
+    // duplicating model settings on TurnContext, but an Op after turn start could update the
+    // session config before this write occurs.
+    let collaboration_mode = sess.current_collaboration_mode().await;
     let rollout_item = RolloutItem::TurnContext(TurnContextItem {
         cwd: turn_context.cwd.clone(),
         approval_policy: turn_context.approval_policy,
         sandbox_policy: turn_context.sandbox_policy.clone(),
         model: turn_context.client.get_model(),
+        collaboration_mode: Some(collaboration_mode),
         effort: turn_context.client.get_reasoning_effort(),
         summary: turn_context.client.get_reasoning_summary(),
         user_instructions: turn_context.user_instructions.clone(),