which addresses this bit, saying that something like “be dych chi’n weld?” is the colloquial form for something like “beth yr ydych chi’n weld?”, which itself is more colloquial than something like “Pa beth yr ydych chwi yn ei weled?”.
It reassures me to see the “ei” in there which matches what I had learned in Cornish It’s just been “optimised out” in spoken Welsh, apparently, possibly leaving behind a soft mutation.