Shell
Also called bash, zsh
The program inside the terminal that reads your line, works out what you mean, starts the right programs and shows you the result. Common ones are bash and zsh. It can also join programs together, and that is most of its power.
An agent's command goes to a shell first, with all its rules, and a stray space or a * means something to it. Those rules are why one wrong character can delete the wrong thing, and why a short line can do far more than it appears to.
Say it to your agent
“This has to work on my Mac and in CI. Start the script with #!/usr/bin/env bash, write it for bash, and run it once with bash explicitly before you tell me it works.”