I always read the "for prim" (a healer who never hurt anyone) as a way for Katniss to hint to Haymitch that she had a plan

She didn't agree to a new hunger games she was faking it. Playing a game to take down both Coin and Snow all at once. It was a smart political move.

I liked this analysis. "For Prim" always stuck out to me because if there's one thing Prim would never, ever have wanted, its a hunger games hosted in her name. So I felt like this was a clue to Haymitch that Katniss had ulterior motives, and that's what makes him consider why she said yes and therefore figure out her plan. It also reveals that Coin never cared about Prim, because if she had she would know this too, which proves that Coin did not care about Prim's fate, which in turn seals Coin's fate.

That makes alot of sense. Haymich always had a stronger bond with Katniss than he did with Peeta, because Katniss and Haymich are soo much alike. I don't think he knew everything that Katniss was up to when she said yes. But he trusted her, that she had a good reason for it.

For me, this scene really cements in how much Katniss’ approach to danger has changed since the beginning of the series. She used to be readable and obvious with her judgments of situations. She handled things physically and/or aggressively. But now, after EVERYTHING, the fact that she can be so casual and cunning in a diplomatic situation really signifies how much her tact has changed.

Katniss has shared everything that was going on in her head throughout the series; the reader has never had to wonder why she did the things she did. However, while "thinking everything through" in that meeting, Katniss conceals her thoughts from the reader for the first time in the series, raising the reader's suspicions and forcing us to wonder what "everything" means. "For Prim" gains her credibility with Coin and gives the reader a temporary reasonable explanation. Haymitch, for his part, is thinking things through as well. He never says yes, but comments "I'm with the Mockingjay." He, too, is boosting Katniss's credibility.

The reason I immediately knew without a doubt that Katniss had a plan behind her “yes” answer is because she would never EVER for any reason agree to this. Not even if the Capitol was actually responsible for killing Prim.

I was so disturbed when Johanna brought up Snow's granddaughter because she was really cute and really liked Katniss.

When she talks to Gale in the the book, about Prim's death and in the end Gale says "shoot straight", for me in that part I knew he wasn't talking about snow.

I always knew the reason for it. I thought it was great and it took Katniss killing Coin for me to realize why she voted yes but my first read through I knew it was to gain her trust. I think it was written that way for Katniss killing Coin to still be a shock but after the shock you realize that was always the plan.

The “for Prim” actually tricked me the first time I read it. I thought Katniss was so lost in despair and anger that she’d basically lost her mind.

I realized it in the movie after her talk with Snow in the movie. Seeing how Coin was turning into Snow before her eyes was what did it for me.

I think Katniss knew she was going to do it after Coin brought up the symbolic hunger games. Because she makes a mention about the arrow that would be used for Snow. She comments about the sharpness and distance of the type of arrow before she goes out.

with the addition of sunrise on the reaping, it is clear haymitch would have never wanting the reaping or hunger games to continue. if not for himself, definitely for lenore dove

This actually makes so much sense. I had already sort of understood why Haymitch and Katniss voted that way. But you laid it out really nicely and it makes a lot of sense the way you broke it down!