A guest's payer rows and recorded payments hung on the users row by ON DELETE
CASCADE, so deleting the guest wiped money that had really moved: expenses
they paid were left without a payer, settled payments reopened, and a custom
or receipt split lost the guest's share so the balances no longer summed to
zero.
Deleting a guest who paid for an expense or is part of a recorded payment is
now refused with a 409 (REST and the delete_trip_guest MCP tool, same text),
and the share dialog says to change the payer or delete the payment first.
Otherwise the guest's share is handed on: an equal split re-splits as before,
a custom amount goes to the others by largest remainder in the currency's
smallest step (members without an amount get one, so the expense stays a
custom split), and a receipt drops the guest from its lines and is split
again like the cost editor does. A legacy paid_by_user_id is cleared as on
account deletion. Account deletion goes through the same re-split. The
confirmation text in all languages and the wiki say what really happens.
Refs #2604
Maurice
1b58acc78f