Kostyuk's 6-1, 6-3 semi-final defeat ended a 17-match winning run on clay this season, a stretch that included a Madrid Open title and a victory over Andreeva in the final.
"For sure, my streak. I take it with me to the grave," Kostyuk told reporters with a smile.
"Very happy with my claycourt season, just one loss. I would never believe it if someone told me this a couple of months ago."
The 15th seed struggled to find her rhythm against a relentless Andreeva, who reached her maiden Grand Slam final, but refused to dwell on the defeat.
"Everything that could go her way went her way. Everything that could not go my way didn't go my way," Kostyuk said.
"I've had enough tough days, bad days to know that they end. It's not the worst thing in the world to lose a match, whatever the stage is."
The loss denied her a first Grand Slam final, but Kostyuk said the emotional high point of her fortnight came after her quarter-final victory against fellow Ukrainian Elina Svitolina, when the Roland Garros crowd responded warmly to her efforts to keep attention focused on Ukraine more than four years after Russia's full-scale invasion.
"I will never forget the ovations that I received after my match in the quarter-finals," she said.
"This is something I will carry with me forever and I will never believe anyone who is at the world stage of this sport saying that they have zero influence.
"If you want to, you can do anything. This was proof for me."
Kostyuk, who has repeatedly spoken out about the war and criticised Russian players, said those moments meant as much to her as her breakthrough run to a first semi-final at a major.
"I'm obviously very happy that I made it to the semi-finals, but I feel like this is the highlight of my tournament," she said of the crowd support.
The 23-year-old also credited years of therapy and self-reflection for helping transform both her tennis and her outlook on life.
"When the full-scale war started, I realised that I needed to change my perspective on life because it's clearly not just tennis," she said.
"The battles that I've won against myself and in my head, Grand Slams are nothing compared to it. Playing tennis is very easy."