What is the ruling on online currency trading through an Islamic account that adheres to the following controls: no usurious interest when holding positions overnight or on cash facilities, margin accounts without lending, and immediate قبض (seizure/possession) and immediate settlement?

The broker who lends the client money in the form of a margin without interest, and stipulates that all of their buying and selling must be done through him, makes the transaction prohibited due to the hadith: "It is not permissible to combine a loan and a sale." However, if the lawful possession (qabd shar'i) is secured, and no overnight charges (rusum al-tabyit) are stipulated, and the broker's role is limited to providing market access, price information, and analyses in exchange for a defined commission, then there is no objection to the transaction.