dirs build() capped the composed path at the 256B pathbuf with a silent
break, so a HOME (or XDG_*) near/over ~240 bytes produced a truncated
path that lookup() then mkdir'd and returned rc=0 — a silently-wrong,
freshly-created directory. ref/hare/dirs/xdg.ha routes through
path::set/push whose too_long error the `!` aborts loudly. Precompute
the composition length in build() and rt_abort when it won't fit; drop
the now-dead silent caps. (Shape (a); routing dirs through lib/path is
the filed fidelity follow-up.)
975_dirs_toolong_run pins the abort + no-stray-dir on both driver twins.
Hojun-Cho
427b67f656