Jax, these sound great -- thank you! I've read Mirror Crack'd and will have to look for the film, as well as that of Masquerade and Malice. I've read about 90% of Agatha Christie's novels, but there are still a few I haven't gotten to yet.
The only Christie plays I've ever seen are The Mousetrap and And Then There Were None. Here's some interesting trivia: Christie wrote 165 short stories, but only 164 of them have been published in the UK. Christie asked that the one that tells the same story as The Mousetrap not be published until after the London run closed. (Both the short story and the play are based on an earlier radio play by Christie.)
I hope to see Witness for the Prosecution at some point. I was debating whether to see it when I was in London in 2019. There is a site-specific run in an old government building that I believe is set up somewhat like a courtroom. I ended up seeing Follies and The Lehman Trilogy instead, which I think was probably the right decision.