Voldemort is lying in parseltongue. He's not going to kill Harry because he can't. He can't because the curse or unbreakable vow he took to not harm himself didn't have release conditions. There was no purpose in putting them in. You don't set up "I can't kill myself unless I try to kill myself", because the 2nd part is useless if the first part works.

"But you tried to end my true life jusst then, sstupid child. Now cursse iss lifted, and I may kill you any time I wissh."

You sir, are a lying liar who lies in parseltongue. Or Harry would be dead right now. Indeed, he would have been dead long ago.

Voldemort is not allowed to kill a version of himself, period. This is how he intended to get around the prisoner's dilemma with his eternal chess buddy. There were to be no clever "Baba Yaga draws Perverelle's blood" outs that would allow someone to murder the foresworn, you were just. not. allowed. Ever. This is the lesson Tom Riddle drew from the story of Baba Yaga; don't leave that loophole. This is what he did with the Goblet of Fire, perhaps?

We would play the game against each other forever, keeping our lives interesting amid a world of fools. I knew a dramatist would predict that the two of us would end by destroying each other; but I pondered long upon it, and decided that both of us would simply decline to play out the drama. That was my decision and I was confident that it would remain so; both Tom Riddles, I thought, would be too intelligent to truly go down that road.

Voldemort would defect in a heartbeat, and he knows it. He has precluded this possiblity, precluded it so strongly that killing Harry or even willing him killed is either impossible to him or would mean his own death.

Note the instructions he gave to his Death Eaters are non-lethal, and varied, and multiplied by dozens of them. He is taking extraordinary non-lethal precautions. He is taking extraordinary measures to resurrect Hermione to prevent a living Harry from destroying the stars. Voldemort is doing this because he wants desperately to not die, and the more obvious option of just killing the idiot-child of foretold destruction is not available to him.