Function relink 

pub fn relink(
    channel: QrPairingChannel,
    config: &Config,
    alias: &str,
) -> Result<RelinkOutcome>

Clear the persisted login state for a channel alias so its next start mints a fresh QR pairing.

Callers resolve their channel type key to QrPairingChannel once via crate::listing::qr_pairing_channel — the same typed key crate::login_probe::persisted_login dispatches on — so probe and relink share one key space and no string key reaches this function. The match below is exhaustive over the feature-gated variant set, so adding a QR-pairing channel without a relink arm is a compile error rather than a silent fallthrough.

Errors are I/O failures from removing existing files (permissions, etc.); absent files are never an error.