ww_ww build writes its intermediates (.combined.ww/.s/.o/binary)
next to the source path. When 995 invoked `ww_ww build /abs/path/
selfhost/cmd/wwdump/main.ww` in parallel with 991/992/994 (which
read selfhost/cmd/<tool>/main.s as a fixture), the build mid-wrote
main.s and the fixture-reading test saw a partial 520B view of the
1.4MB file → "C 1422712 vs ww 520 bytes" assembler-byte-diff fail.
The race was latent pre-31594e4 too: parallel test/run + serial
995 always finished 995 last (3min wall), so 991 was already done
by the time 995's wwdump build wrote main.s. Internal-parallel 995
finishes in 1m47, opening the window.
Fix: cp the source to <workdir>/build.ww before invoking ww_ww,
build from build.ww. Driver writes intermediates as build.{combined.ww,
s,o} and binary `build` in workdir; canonical selfhost/cmd/<tool>/
main.* are never touched by 995. Imports still resolve via -I, but
those paths are read-only fixtures.
Verified 3 consecutive `make test` runs 132/132 (4:18, 3:22, 3:16).
Hojun-Cho
be363f4451