Function reconcile 

pub fn reconcile(
    vault_path: &str,
    signers: &BTreeMap<String, String>,
    currently_signed: bool,
) -> PinVerdict

Reconcile the vault’s current signer registry against the local pin.

Returns Conflict when an already-pinned pubkey now maps to a different verifying key. Otherwise records any new pubkeys and returns Ok with the set of first-seen (trust-on-first-use) signers, plus downgraded — the vault was signed before on this machine but is unsigned now. currently_signed is whether this load carried a valid signature. When pinning is unavailable (opted out, or no home dir) every signer is first-use and no downgrade is reported, since nothing is anchored.