test: split fast/full, parallelize 995, race-correct two-phase test/run

test/run fans out test/wcc/*.c except 950 and 990-997 across $(nproc)
xargs workers, then runs the byte-id gates sequentially in phase 2.
Each worker writes <prefix>.status into a mktemp results dir; the
collector emits them in glob order for deterministic output. Phase 2
sequentiality sidesteps the race introduced by ww_ww writing
intermediates next to every traversed source (#15) — concurrent reads
of selfhost/cmd/<tool>/main.{combined.ww,s,o} would see partial bytes
(#16).

`make test-unit` (UNIT=1) skips phase 2 entirely for a 3.8s inner-loop
check; `make test` runs the full 132 in ~8:30. test-unit goal aligns
with the selfhost-bootstrap project goal: 990-997 + 950 are the
toolchain-rebuild gates, fast feedback is for unit work below them.

990-995 wrap every ww/w6c/w6a/w6l/wwdump invocation in `timeout 180`;
995's hardcoded /tmp/ww_d_hello.ww is now pid-keyed. 995 forks its 5
ww_ww builds concurrently (waitpid for collection) so its solo wall
drops from 3:15 to 1:32. Phase-2 split (parallel readers + sequential
writers) deferred to #17, post #15.

Wall: 9:59 → 8:32 (full) / 3.8s (test-unit, ~158× from baseline).

test/run

@@ -46,15 +46,34 @@ trap 'rm -rf "$RESULTS"' EXIT
 
 JOBS=${JOBS:-$(nproc 2>/dev/null || echo 4)}
 
-# Emit (prefix, testpath) pairs NUL-separated. The prefix carries the
-# test's <NNN>_<name> stem so the collector iterates in lexical order,
-# yielding deterministic output even though workers interleave.
+# Phase 2 runs the wwstage byte-id gates (990-997) + 950_selfcheck
+# sequentially. ww_ww writes intermediates next to every traversed source
+# (task #15), so 991/992/994's reads of selfhost/cmd/<tool>/main.{s,o,
+# combined.ww} race against any concurrent driver-using test that emits
+# a sibling .combined.ww (task #16). Phase 1 stays parallel for unit
+# coverage; phase 2 sequential keeps the byte-id gates honest.
 for t in test/wcc/*.c; do
 	[ -f "$t" ] || continue
+	case ${t##*/} in
+	950_*|990_*|991_*|992_*|993_*|994_*|995_*|996_*|997_*) continue ;;
+	esac
 	name=${t##*/}; name=${name%.c}
 	printf '%s/%s\0%s\0' "$RESULTS" "$name" "$t"
 done | xargs -0 -n2 -P "$JOBS" "$0" --one || true
 
+# UNIT=1 (make test-unit) is the inner-loop short path: skip the wwstage
+# byte-id gates (990-997) and 950_selfcheck entirely. Pre-push uses
+# `make test` for the full suite.
+if [ "${UNIT:-0}" != "1" ]; then
+	for t in test/wcc/950_*.c test/wcc/990_*.c test/wcc/991_*.c \
+	         test/wcc/992_*.c test/wcc/993_*.c test/wcc/994_*.c \
+	         test/wcc/995_*.c test/wcc/996_*.c test/wcc/997_*.c; do
+		[ -f "$t" ] || continue
+		name=${t##*/}; name=${name%.c}
+		"$0" --one "$RESULTS/$name" "$t" || true
+	done
+fi
+
 fail=0
 ran=0
 for s in "$RESULTS"/*.status; do