ctrl+r

Hitting ctrl+a ctrl+r ^[?] allows you to choose a command from your command history and insert it into your current pane. This works just like fzf, atuin, hstr, et al, but it also gives you a preview of what the screen looked like when you executed that command.

You can also use the same interface to open a particular command from your history in replay mode using the ctrl+a f ^[?] binding. In effect, you can jump back to the exact moment in time you executed any command.

Why not bind this directly in the shell?

Most programs that replace the default ctrl+r functionality require you to overwrite the existing key binding, typically through per-shell configurations. The advantage of doing this at the level of the terminal multiplexer (as opposed to configuring individual shells) is that cy's ctrl+r works anywhere: in editors, over SSH, et cetera. It does not matter what system you're on, you can still just hit ctrl+a ctrl+r ^[?] and insert a command from your history.

Another subtle advantage is that once you've put cy's command detection sequence in your prompt on a system, you will never need to update it. In the example of a remote system, cy need not even be installed; when you connect from cy, command detection will work even if the remote does not have cy.