Constant TIER_TASK_TCB_U64S 

pub const TIER_TASK_TCB_U64S: usize = 64;

issue 1598 — the control-block region every TierTaskMemory carries, in 8-byte words. An UPPER BOUND over the kernels that take it (a FreeRTOS StaticTask_t on Cortex-M is about a hundred bytes); the port REFUSES a region smaller than its own control block at spawn, by name, so a kernel whose block outgrows this fails loudly rather than overrunning the stack that follows. Rust cannot name a C type’s size at macro time, which is why this one number is a bound and the stack beside it is exact.