Constant COUNTER_MAX_VALUE 

pub const COUNTER_MAX_VALUE: u32 = 2_097_151;

Maximum supported counter value on the ATECC608B (2^21 - 1).

Each successful “key-usage event” against a slot whose LimitedUse bit is set bumps the counter by one. When the counter reaches this ceiling the chip refuses further increments. The value is fixed by the chip’s storage size (21 bits encoded in the 8-byte structure).