Function read_done_count 

pub fn read_done_count(control_bytes: &[u8]) -> u32

Decode the kernel’s done_count from a control buffer.

On a malformed or truncated control buffer this returns 0 and emits a tracing::error! so the stall is operator-visible. Prefer try_read_done_count in new code, a silent 0 is indistinguishable from the initial kernel state and can cause the host pump to stall indefinitely.