Constant INVOKED 

pub const INVOKED: u32 = 512;

An invoked worker (crate::invoke): HELLO carries, after the most shards to hold, the invocation’s ID u64. The server grants that invocation’s free shards at once, never more and never later (no standby), or refuses the connection. The lease parameter is remaining_ms u32, the invocation’s budget left. Granted with SHARD_LEASES only. The worker drains (DRAIN) and reports (IDLE) before it leaves.