Hello, ash cannot tab-complete built-in commands as it does with commands in $PATH. For example: $ bre<tab> does not show break. The same happens for all built-in commands that does not have a stand-alone binary (like echo) in $PATH (even if busybox). bash, ksh and csh all tab-complete built-ins.
Fixed in git: commit 9e2a5668fd38db169d9d91b13089a99df4c9bd37 Author: Ron Yorston <rmy@pobox.com> Date: Tue Jan 21 16:01:58 2020 +0000 ash,hush: allow builtins to be tab-completed