What is that autosuggest magic?

zsh-autosuggestions ↓

https://github.com/zsh-users/zsh-autosuggestions

If you press the → key (forward-char widget) or End (end-of-line widget) with the cursor at the end of the buffer, it will accept the suggestion, replacing the contents of the command line buffer with the suggestion.

If you invoke the forward-word widget, it will partially accept the suggestion up to the point that the cursor moves to.

What is that forward-word magic?

Manual install ↓

https://github.com/zsh-users/zsh-autosuggestions/blob/master/INSTALL.md#manual-git-clone