No worries Azira re: the replies (I'm not sure that mine are helping so much as creating more questions).
They can fly well, and a small barrier at their height, or even much higher, will do nothing to stop them getting out if a door is open. They are also very fast when they feel the need to get past you. They could easily fly over your head or through your legs. Once they're comfortable around you, they will think nothing of going straight past you as you open the door & stick your arm or arms in.
My brain has been in overdrive to come up with a solution for an A-frame. I think I'd make the door or doors as small as possible & get a large aquarium net to catch quail in the pen when you need to. The door should be just big enough to get the net through. That would also help to pick up eggs, as they may lay anywhere, or they may end up choosing one or two favourite spots to lay if there's somewhere they're happy with. You want the net handle to be long enough to easily reach all points in the A-frame, which will partly depend on how far you can get your hand & arm in.
Separately, I'd hinge one entire side for opening to clean it out. If you put in deep litter you won't need to do that much at all. Or just put them on grass & move the A-frame onto new grass periodically.
Oh.. and the size of the covered end (if it's going to go all the way to that 'middle' frame) will be plenty without a baffle of any sort. I'd just stick their feeder or waterer there, which will be a small visual barrier for them to get behind if they want to get away from a predator's line-of-sight a bit.
For changing water & putting in feed, you need to decide whether you'll have containers that you can refill from outside, without opening either the small doors or the larger hinged side. I'd set it up so that you can do that if at all possible. Water can be in the open area, and food can be put in a container under cover, or scattered about for them to search for (but that means careful balancing of ENOUGH food without so much that you create problems of mouldy or off food which would create health problems for them). If you open the larger hinged side I would ALWAYS get the quail out first & put them into a secure smaller carrier whilst you sort out whatever you're doing in the A-frame.
If you get to put them in an aviary later, then I would do that. You can still utilise the A-frame as their temporary enclosure when doing things in the aviary. If you have a birdlock in the aviary you get, you won't need the A-frame for that, but it will still come in handy for some time... or you could sell it as a chook broody cage.
Thoughts going around in circles here... you can still shoo them to the other end of the pen to a degree... and the more you handle them & catch them, the better you'll come to understand how they can move & avoid them getting out. Depends how quick you think you'll learn that.