Function reconcile 

pub fn reconcile(
    repo: &Path,
    source_records: &[MigrationRecord],
) -> Result<ReconcileReport, String>

Reconcile a source’s extracted records against the store. The store-side key is read from each the derived key of its non-hashed source_ref if present, else the first round/#N token in the hashed observe — so the join is durable (NOT dependent on the events log). A source key with no store match is a SOURCE-ONLY gap (the capture gap to surface); a store key with no source match is STORE-ONLY; a store tick with no derivable key is counted separately as un-keyable.