That distinction (i.e. debit having less fraud and bad merchant behavior protections) is largely a myth: You get chargebacks and zero liability on effectively all debit cards these days.

Both credit and debit policies by almost all banks exceed the legal requirements a lot (e.g. no issuer that I know actually charges the deductible allowed by law).

Edit actually answering your question: Go2Bank.com

Most Americans just call this a checking account.

> According to the Fed’s 2022 Economic Well-Being of U.S. Households survey released Monday, some 37% of Americans lack enough money to cover a $400 emergency expense, up from 32% in 2021. That means nearly one in four consumers would have to use credit, turn to family, sell assets, or get a loan in order to cover any major unexpected cost.

My credit union lets me open up sub accounts. I can set rules for the sub accounts. I can get a card that only draws from a sub account. This is all free.

I'd kill for my CU to be a part of that network.

Most checking accounts have a feature that lets you transfer X amount from Y external account when Z happens.

Most?

I must be the most unlucky person in banking history; I've yet to see this across 6 banks.

What banks are doing conditional anything, on any inputs besides time-frequenced wires?

I've seen this as a basic feature on at least two banking sites: "when the balance gets below $X, move $Y amount to that account." If you have more than one account with that bank then you can also choose the source of that money.

Often it's a part of the overdraft settings.

I’ve only ever seen “when a payment can’t be covered on account x, take the exact sum out of account y”, which together with a maximum number of savings withdrawals per month doesn’t really work like the feature GP wants.

At least two banks I've used have "low cash mode", where they notify you and make a transfer if your balance goes below a certain amount.

Interesting, is this in the US? Would you mind sharing which, if so?

I'd rather not say the exact bank, but let's say a mid-range bank in the Midwest.