Constant FUTURE_SLOT_POLL 

pub const FUTURE_SLOT_POLL: usize = 0;

The future value’s own layout – the { poll_code, state } two-word fat pointer every nova_rt_task_spawn / nova_rt_task_block_on argument points at, the same shape MakeClosure builds for a closure. Named for the same reason STATE_SLOT_TAG and friends are: async_lower.rs (Task 5) builds this layout independently and the two ends are kept in step by nothing but these declared offsets.

• FUTURE_SLOT_POLL (offset 0): the PollFn’s address.
• FUTURE_SLOT_STATE (offset 8): the state object’s address.