Settle-up & re-sharing (Splitwise-style)

Track running balances between household members — “Alice owes Bob $X this month”. A settle-up action creates either a real transfer transaction (if both users have a suitable shared/personal account) or a balance entry in a dedicated settle-up ledger. Closes the loop on per-user transaction splits.

Also unlocks re-sharing: users with the manage permission can invite further members, not just the resource owner.

Depends on per-user transaction splits being delivered first (see the umbrella for that sub-feature).

Part of: https://moneymatter.featurebase.app/p/household-sharing-umbrella