[2/3] core: persist world state in rollouts

[sayan-oai]

Why

WorldState currently remembers its model-visible diff baseline only in memory. That leaves no durable source for restoring the exact baseline after resume, fork, rollback, or compaction.

This is the second PR in the WorldState persistence stack, built on #29833 and following #29249. It records durable state transitions; the next PR will replay them during rollout reconstruction.

What

• Add a world_state rollout item containing either a full snapshot or an RFC 7386 JSON Merge Patch.
• Persist a full snapshot after initial context and after compaction establishes a new context window.
• Persist non-empty patches when later sampling steps or turns advance the WorldState baseline.
• Write model-visible history before its matching WorldState record, so an interrupted write can only cause a safe repeated update on replay.
• Preserve WorldState records for full-history forks while excluding them from thread previews, metadata, and app-server history materialization.

Older binaries read rollout lines independently, so they skip the unknown world_state records while retaining the rest of the thread.

Testing

• just test -p codex-core snapshot_merge_patch_changes_and_removes_nested_values
• just test -p codex-core world_state_baseline_deduplicates_until_history_is_replaced
• just test -p codex-core deferred_executor_compaction_preserves_then_updates_environment_once
• just test -p codex-protocol
• just test -p codex-rollout
• just test -p codex-state
• just test -p codex-thread-store
• just test -p codex-app-server-protocol

[chatgpt-codex-connector]

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[jif-oai]

lgtm