Function ready 

pub(crate) fn ready(stalled: Option<(&'static str, u64)>) -> Response

Readiness is one question: can this instance accept an export and make it durable? Everything else about the process is /health’s.

Split from the handler so both answers are testable without a disk that has actually filled up — and so the only input is the one fact the decision turns on. The threshold itself is pipeline::UNREADY_AFTER, and its whole job is to make this a sustained condition: a probe that flips on one failed publish would deregister a node for every EIO and every restart of the volume underneath it, and an endpoint list that changes every ten seconds costs more exports than the node it was protecting.