chore(linux): address review comments

This change also slightly modifies `echo_heading` and outputs a
mark. This will show to the left of the line as well as in the
scroll bar in a terminal in VSCode [[1]] and will help to find the
headings if you have a lot of output in between.

[1]:https://code.visualstudio.com/updates/v1_69#_setmark-sequence-support