If you're rly interested I'd suggest reading Cope's book, as he lays out the figures and even the movement of the money better than I can with more citations than I can. As you suggest, it's about the aggregate motion of capital. Take your restaurant example:

The restaurant isn't losing money so long as imperialism persists, because they're selling e.g. burgers for inflated prices. The burgers can be sold for inflated prices because e.g. construction worker is paid inflated wages. Construction company can afford to pay inflated wages because it's buying artificially cheap materials and because it's being paid inflated fees by e.g. a bakery. Bakery can pay the inflated fees because it's buying artificially cheap materials and because it's selling e.g. cakes at inflated prices. The cakes can be sold for inflated prices because e.g. tech employees are paid inflated wages. Tech companies can afford to pay employees inflated wages because e.g. government buys new windows hardware at inflated prices. Government can afford those inflated prices because a. the global south governments pay them yearly debt repayments or b. because they tax superprofit made in the global south.