The chip derivation was TrimEnd(separator), which is a name only for the
Windows drives it was written against: on Unix it made the / chip an empty
pill and the home chip the entire home path, drawn at full width in a header
column nothing bounds. A home directory deep enough — CI's per-job HOME is
forty-six characters — had that one chip walk the header's own buttons out of
the window at the session shell's 472-pixel budget, which is the half of the
runner's red suite the star-column fix before this one did not reach.
A chip says C:, /, ~, or a mount's last segment now; the full path stays on
its command parameter, where length costs nothing. RootChipNameTests pins the
derivation with fixed strings, so it no longer takes a machine with a deep
profile path to ask the question.
