What it is: Capture/restore JSON for unique per-instance item payload (InventoryItemInstance.ComponentStates), used with InventoryItemData.Supports Instance State. Files: IInventoryItemState.cs, InventoryItemStateBehaviour.cs, InventoryItemStateUtility.cs.
How to use: Enable Supports Instance State on item data; implement capture/restore on the world prefab; pickup/drop pipelines call the utility to pack/unpack state into the container save blob.
Full walkthrough (weapon ammo example): InventoryItemState.md (Russian).