eshell-deferrable-commands

eshell-deferrable-commands is a variable defined in `esh-cmd.el'.
Its value is

(eshell-named-command eshell-lisp-command eshell-process-identity)

• This variable may be risky if used as a file-local variable.

Documentation:
A list of functions which might return an asynchronous process.
If they return a process object, execution of the calling Eshell
command will wait for completion (in the background) before finishing
the command.

You can customize this variable.