diff --git a/test/run b/test/run
index 3dd97a73..186d79b0 100755
--- a/test/run
+++ b/test/run
@@ -46,12 +46,12 @@ trap 'rm -rf "$RESULTS"' EXIT
 
 JOBS=${JOBS:-$(nproc 2>/dev/null || echo 4)}
 
-# 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.
+# Phase 2 runs the wwstage byte-id gates (990-997) + 950_selfcheck.
+# 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; the
+# wwstage-driver tests stay out of phase 1 to keep those reads honest.
 for t in test/wcc/*.c; do
 	[ -f "$t" ] || continue
 	case ${t##*/} in
@@ -65,9 +65,27 @@ done | xargs -0 -n2 -P "$JOBS" "$0" --one || true
 # byte-id gates (990-997) and 950_selfcheck entirely. Pre-push uses
 # `make test` for the full suite.
 if [ "${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
+	# Phase 2 is partitioned (#3): the pure-reader byte-id gates run in
+	# parallel; the source-tree writers run in a serial tail afterward.
+	#
+	# PARALLEL GROUP — 990/991/992/994/996/997. Each reads only committed
+	# or make-all-produced files and writes only /tmp or a disjoint tracked
+	# stem (990→out smoke.*, 996→examples/mandelbrot/*, 997→/tmp fixture
+	# copy). No group member writes a stem another member reads (per-gate FS
+	# footprint audited race-free, #3), so they fan out via the same
+	# xargs -P "$JOBS" machinery as phase 1.
+	for t in test/wcc/990_*.c test/wcc/991_*.c test/wcc/992_*.c \
+	         test/wcc/994_*.c test/wcc/996_*.c test/wcc/997_*.c; do
+		[ -f "$t" ] || continue
+		name=${t##*/}; name=${name%.c}
+		printf '%s/%s\0%s\0' "$RESULTS" "$name" "$t"
+	done | xargs -0 -n2 -P "$JOBS" "$0" --one || true
+
+	# SERIAL TAIL — 993/995/950, the only source-tree writers. 993 & 995
+	# both write cmd/wwdump/main.* (995 writes all 5 cmd/*/main.*), so they
+	# run sequentially w.r.t. each other AND after the parallel group, so
+	# the group's readers see stable make-all output, never a torn write.
+	for t in test/wcc/993_*.c test/wcc/995_*.c test/wcc/950_*.c; do
 		[ -f "$t" ] || continue
 		name=${t##*/}; name=${name%.c}
 		"$0" --one "$RESULTS/$name" "$t" || true