I have just been watching a video of Robin Thomson making sourdough at the Beshara School:
He makes a very slack dough, kneads it using the “French” method (more or less) and adds a rather large quantity of starter after he has developed the dough. After more kneading he then adds salt stating that “salt must never come into contact with sourdough starter” and maintaining that the addition of salt prevents the starter from performing its function. Several other experts also advise delaying the addition of salt until the dough is developed (whether by kneading or stretch and fold).
I have been making sourdough successfully on a weekly basis for a couple of years now and my method involves making a preferment, which I leave overnight, then adding all the water and stirring in the salt before adding the main quantity of flour and kneading for ten minutes.
My reasoning is that the salt dissolves more easily this way and the method seems to work well but I would be very interested to know whether there is a scientific justification for not adding salt until later in the process or whether it is simply received wisdom.