Record the initial AutoCompactWindowIds window_id in session_meta.context_window so JSONL tailers can observe the first context window before any compaction item exists. Thread creation now requires an initial_window_id string, while rollout JSONL keeps that value under the context_window namespace without writing derived chain fields for the initial window.
Rollout reconstruction derives window 0 state from that initial_window_id when no compaction window metadata exists. Forks intentionally use the same reconstruction path; consumers that need to distinguish copied initial-window metadata can use thread_id. Legacy compactions without window_number continue to use compaction-count fallback accounting.
Verification:
- just test -p codex-protocol
- just test -p codex-rollout recorder_materializes_on_flush_with_pending_items
- just test -p codex-core reconstruct_history_restores_initial_window_from_session_meta
- just test -p codex-core reconstruct_history_prefers_compacted_window_over_session_meta
- just test -p codex-core reconstruct_history_preserves_legacy_compaction_count_with_session_meta_window
- just test -p codex-core reconstruct_history
- just test -p codex-core record_initial_history_reconstructs_forked_transcript
- just test -p codex-thread-store
- just test -p codex-state
- just test -p codex-app-server thread_read_returns_summary_without_turns
- just test -p codex-rollout persistence_metrics
- just fix -p codex-protocol -p codex-rollout -p codex-thread-store -p codex-core -p codex-app-server
- just fix -p codex-core -p codex-rollout
- just fix -p codex-core
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