After lengthy negotiations in Brussels, European diplomats proposed a limit on the price of Russian oil Friday, a move lauded by the Biden administration that has long sought to hit the Kremlin’s energy revenue without wreaking additional havoc on markets. If the Group of Seven nations and Australia concur, it will take effect Monday — the same day the European Union’s embargo on Russian seaborne crude goes into force. It remains unclear whether the move will hit Moscow’s finances, since the $60-per-barrel cap is so close to current prices.