How to pipe into zsh with alias expansion?

Piping code into zsh runs that code in a separate process. This process doesn't have your interactive settings such as aliases and functions (it doesn't read .zshrc) and doesn't have the shell variables and other state of the current shell. The state of that other process, such as the current directory, is lost when that process exits.

To execute code in the current shell process, pass it as an argument (not as input) to the eval builtin.

eval "$(<~/.zsh_history cut -d ';' -f 2 | sk --tac)" 

But for this specific use case of selecting a history entry, there's an other way. The fc builtin. The following command runs the function fcedit_sk with one argument, which is the name of a temporary file. When the function is called, the file contains all the history entries (${${(kn)history}[1]} is the index of the oldest entry and -1 means the newest entry). When the function returns, zsh executes whatever the file contains as if you had entered it at the prompt.

fc -e fcedit_sk ${${(kn)history}[1]} -1 

Make fcedit_sk a function that calls sk on the content of the file and writes its output back to the file. I don't know sk, so I don't know if there's an easier way than this:

fcedit_sk () { local output output=$(sk --tac <$1) if (($?)); then echo >|$1 # Cancelled else print -lr -- $output >|$1 fi }