Auto-apply a match only when it's mutually unique — everything else goes to a person

Context

Bank reconciliation pairs each bank statement line with the ledger entry it corresponds to. Most pairs are obvious. Some aren't: two payments of the same amount a day apart, or a cheque that cleared three days after it was booked. A matcher that picks "the closest" in those cases will sometimes pick wrong — and a wrong reconciliation is harder to find than an unreconciled line.

Decision

A match is applied automatically only when it is mutually unique: the statement line has exactly one eligible ledger candidate within tolerance, and that ledger entry has exactly one eligible statement line. Tolerance is the exact amount within a few days either side. Anything else is shown as a low-confidence suggestion — closest by date — for a person to confirm. Only unreconciled entries are ever candidates. A statement line with no ledger entry at all (a bank charge, interest) offers a one-click journal entry.

Why

Mutual uniqueness is a condition the matcher can prove, not a score it has to trust. When it holds, there is no second interpretation to get wrong. When it doesn't, the ambiguity is real information a person should see, not noise to be resolved by a tie-break rule.

Trade-off

A month with many identical amounts — standing instructions, equal instalments — auto-matches less and leaves more for a person to click through. That's the intended cost: the manual queue grows exactly where a guess would have been riskiest.

tolerance

exact amount, ±3 days for clearing lag

auto-applied when

exactly one eligible candidate on each side

self-check assertions

8, including "ambiguous candidates stay low confidence"