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 action/jump-history-command action. 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.