I have an idea that might tame the great lengths of halyard that accumulate in the cockpit when a junk sail is raised.
If the tail of the halyard is attached to/becomes the tail of/ a multipurchase downhaul, almost all the halyard can be taken up in the multiple downhaul loops attached to the bare battens of a SJR where they pass the mast. With (for example) an 8-panel sail the end of the downhaul is attached to the bottom batten/boom (8), passes under a block at the deck, goes up to a block on batten 7, down to the deck again, up to batten 5, deck, 3, deck, yard, deck. The last downward pass from the yard goes under one more block and the downhaul tail becomes the halyard tail; there is no bitter end to either line. For 8 battens at 5ft spacing and a 5:1 halyard purchase, this reduces the halyard tails from 200 ft of loose end to a loop of at most 45ft, including a bit of margin to have some slack at the tightest point reached in mid-haul.
Only this loop of halyard/downhaul tail needs to be managed at the helm station. When hoisting the sail, the downhaul camcleat needs to be released so that the yard can lift the sail, but conversely if the halyard is released its tail can pull more line from the downhaul through that camcleat without the helmsman needing to take any action. This allows an emergency stop just by releasing the halyard's camcleat.
For reefing, the halyard is paid out and the downhaul pulled in, pulling every other batten down until it lands in the sail catcher. Once a batten lands, the downhaul tail supply rate drops relative to the halyard's constant tail demand, and the loop of excess cord shrinks. When the yard lands in the sailcatcher, only the extra loop of tail remains. Thus there is never a huge inventory of cordage to be stowed at the helm. The total number of downhauls on the battens can be selected to provide a reasonable (although varying) match to the amount of halyard tail that is freed up when the yard is lifted. By threading the downhaul through the battens' blocks from the bottom up, as each batten lands the downhaul no longer needs to move relative to it and can't get bound up to prevent hauling on the still-aloft battens.
If the downhaul is tightened before gybing, it should serve as a fan-up preventer by holding the idle battens down. The bottom batten/boom can be supported by a collar around the mast, no mast lift is needed, and the boom can be as close to the deck as desired. No allowance should be needed for a vang since the downhaul and the offcenter weight of the sail will hold the boom down against the collar, and the entire sail forward against the tight-fitting batten parrels.