core: assign item IDs to compacted replacement history

[pakrym-oai]

Why

Remote v2 compaction can return replacement-history items without IDs. Because replacement history is installed directly, those items bypass normal history preparation and remain ID-less in later Responses requests even when the item_ids feature is enabled.

What changed

• Pass the active TurnContext into replace_compacted_history.
• When item_ids is enabled, assign missing IDs before installing and persisting replacement history.
• Rebuild CompactedItem from the prepared history so live and persisted replacement histories match.
• Add integration coverage requiring IDs on every ID-capable input item in the initial, remote v2 compaction, and post-compaction requests.

Test plan

• just test -p codex-core response_item_ids
• just test -p codex-core websocket_v2_test_codex_shell_chain
• just test -p codex-core remote_compaction_parity_pre_turn_auto
• just test -p codex-app-server thread_inject_items_adds_raw_response_items_to_thread_history

[chatgpt-codex-connector]

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