Function persist_node_id
pub fn persist_node_id(data_dir: &Path, id: &str) -> Result<()>Expand description
Atomically persist the effective node-id to <data_dir>/relay/node_id (temp +
rename), so a concurrent reader (ensure_node_id / relay_profile) never sees
a half-written value. This is what makes a rotated id flow to clients in-band
on their next renewal.