why not use something like in via ferrata sets - a single easy-to-open carabiner with a short cord, attached to you. when you climb a ferrata, you clip&unclip hundreds of times, nothing particularly complicated or taxing, and in water you would need only a basic one with little resistance on the gate opening part.

you could pass along the cable holding the carabiner in one hand, not slowing you down

You could pass a tie-off if you had two carabiners, as you do in via ferrata. Don't know about the entanglement risk though... I'm not a diver but that sounds way less dangerous to me than losing the cable altogether, since worst case you could just release the carabiner