[codex] Remove unused TurnContextItem fields

[pakrym-oai]

Why

TurnContextItem is the durable baseline used to reconstruct context diffs across resume/fork. Several fields persisted on it were no longer read from the persisted item: trace ids, reasoning summary, user/developer instructions, output schema, and truncation policy. Keeping them in rollout snapshots adds schema surface and state that can drift without affecting reconstruction.

What changed

• Removed the unused persisted fields from TurnContextItem.
• Stopped writing those fields from TurnContext::to_turn_context_item.
• Updated rollout/context reconstruction fixtures and the trace-id unit test to assert the live TurnContext trace id instead of carrying it through TurnContextItem.

Verification

• cargo test -p codex-protocol --lib turn_context_item
• 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-rollout resume_candidate_matches_cwd_reads_latest_turn_context
• cargo test -p codex-state turn_context
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep new rollout turn_context lines readable by older builds

When a user creates turns with this version and then opens/resumes/forks the same rollout with the currently released older binary, the older TurnContextItem still requires summary, so RolloutRecorder::load_rollout_items fails to deserialize and skips each new turn_context line. That drops the persisted previous-turn settings/reference context baseline used for resume/fork reconstruction, so model/realtime/context diffs are rebuilt as if no baseline existed; if rollout compatibility across versions is expected, keep serializing at least the default summary until older readers make it optional.

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[chatgpt-codex-connector]

Update the remaining suite TurnContextItem constructor

This struct shape change leaves core/tests/suite/resume_warning.rs:28 constructing TurnContextItem with the removed trace_id, summary, user_instructions, developer_instructions, final_output_json_schema, and truncation_policy fields. Building the core integration suite now fails with unknown-field errors for that test target, so the removed fields need to be deleted there as well.

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[github-actions]

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1 out of 2 committers have signed the CLA.
✅ (pakrym-oai)[https://github.com/pakrym-oai]
❌ @alexburch-oai
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