[codex] Trim unused TurnContextItem fields (#22709)

## Why

`TurnContextItem` is the durable baseline used to reconstruct context
diffs across resume/fork. Most of the old persisted-only fields on it
are no longer read, so keeping them in rollout snapshots adds schema
surface and state that can drift without affecting reconstruction.

`summary` is the exception: older Codex versions require it to
deserialize `turn_context` records, so keep writing a default
compatibility value until that schema surface can be removed safely.

## What changed

- Removed the unused persisted fields from `TurnContextItem`: trace ids,
user/developer instructions, output schema, and truncation policy.
- Kept `summary` with a compatibility comment and made
`TurnContext::to_turn_context_item` write `ReasoningSummary::Auto`
instead of live turn state.
- Updated rollout/context reconstruction fixtures for the retained
summary field.

## Verification

- `cargo test -p codex-protocol --lib turn_context_item`
- `cargo test -p codex-rollout
resume_candidate_matches_cwd_reads_latest_turn_context`
- `cargo test -p codex-state turn_context`
- `cargo test -p codex-core --lib
new_default_turn_captures_current_span_trace_id`
- `cargo test -p codex-core --lib
record_initial_history_resumed_turn_context_after_compaction_reestablishes_reference_context_item`
- `cargo test -p codex-core --test all
emits_warning_when_resumed_model_differs`
- `git diff --check`

codex-rs/state/src/extract.rs

@@ -156,7 +156,6 @@ mod tests {
     use chrono::DateTime;
     use chrono::Utc;
     use codex_protocol::ThreadId;
-    use codex_protocol::config_types::ReasoningSummary;
     use codex_protocol::models::ContentItem;
     use codex_protocol::models::ResponseItem;
     use codex_protocol::openai_models::ReasoningEffort;
@@ -339,7 +338,6 @@ mod tests {
             &mut metadata,
             &RolloutItem::TurnContext(TurnContextItem {
                 turn_id: Some("turn-1".to_string()),
-                trace_id: None,
                 cwd: PathBuf::from("/parent/workspace"),
                 current_date: None,
                 timezone: None,
@@ -353,11 +351,7 @@ mod tests {
                 collaboration_mode: None,
                 realtime_active: None,
                 effort: None,
-                summary: ReasoningSummary::Auto,
-                user_instructions: None,
-                developer_instructions: None,
-                final_output_json_schema: None,
-                truncation_policy: None,
+                summary: codex_protocol::config_types::ReasoningSummary::Auto,
             }),
             "test-provider",
         );
@@ -379,7 +373,6 @@ mod tests {
             &mut metadata,
             &RolloutItem::TurnContext(TurnContextItem {
                 turn_id: Some("turn-1".to_string()),
-                trace_id: None,
                 cwd: PathBuf::from("/fallback/workspace"),
                 current_date: None,
                 timezone: None,
@@ -393,11 +386,7 @@ mod tests {
                 collaboration_mode: None,
                 realtime_active: None,
                 effort: Some(ReasoningEffort::High),
-                summary: ReasoningSummary::Auto,
-                user_instructions: None,
-                developer_instructions: None,
-                final_output_json_schema: None,
-                truncation_policy: None,
+                summary: codex_protocol::config_types::ReasoningSummary::Auto,
             }),
             "test-provider",
         );
@@ -413,7 +402,6 @@ mod tests {
             &mut metadata,
             &RolloutItem::TurnContext(TurnContextItem {
                 turn_id: Some("turn-1".to_string()),
-                trace_id: None,
                 cwd: PathBuf::from("/fallback/workspace"),
                 current_date: None,
                 timezone: None,
@@ -427,11 +415,7 @@ mod tests {
                 collaboration_mode: None,
                 realtime_active: None,
                 effort: Some(ReasoningEffort::High),
-                summary: ReasoningSummary::Auto,
-                user_instructions: None,
-                developer_instructions: None,
-                final_output_json_schema: None,
-                truncation_policy: None,
+                summary: codex_protocol::config_types::ReasoningSummary::Auto,
             }),
             "test-provider",
         );