diff --git a/Makefile b/Makefile
index d6169a40..6c69ba02 100644
--- a/Makefile
+++ b/Makefile
@@ -3256,7 +3256,7 @@ sizelint:
 peellint:
 	@sh tools/peellint
 
-test: all sizelint peellint $(TESTS) test-lang test-lang-byteid
+test: all sizelint peellint $(TESTS) test-lang test-lang-byteid test-run
 	@WW=$(BIN)/ww BIN=$(BIN) sh test/run
 
 test-unit: all sizelint peellint $(TESTS)
@@ -3264,12 +3264,22 @@ test-unit: all sizelint peellint $(TESTS)
 
 # ---- test-run: ww-native behavior harness (fold 2) ---------------------
 # Drives test/runww.ww over every test/wcc/data/<name>/case.ww, building
-# and running each case through the cstage `ww` driver (T1) and checking
-# its leading `//ww:` directive. The harness prints `runww: all ok` and exits
-# 0 only if every case passes; the target propagates that exit code. NOT
-# yet wired into `make test` (fold 6). See test/runww.ww header.
+# and running each case through the cstage `ww` driver (T1, plus the ERROR
+# arm's wwstage w6c_ww leg) and checking its leading `//ww:` directive. The
+# harness prints `runww: all ok` and exits 0 only if every case passes; the
+# target propagates that exit code. Wired into `make test` (pre-push only).
+#
+# runww execve's its child `ww`/`w6c_ww` with a NIL envp, so a WW_PKGCACHE=
+# override can't reach them — the children write the DEFAULT out/.pkgcache,
+# the same cache the recipe's $(TESTS)/byte-id gates use. The order-only
+# prereqs (after `|`) force `make test -j` to schedule test-run strictly
+# LAST among the prereqs, so it cannot run concurrently with any default-
+# cache writer (`all`'s selfhost builds are already ordered via the normal
+# `all` prereq; test-lang/test-lang-byteid use isolated caches, but ordering
+# after them is belt-and-suspenders). The recipe's 990-997/pkgcache default-
+# cache tests run only after ALL prereqs complete, so no overlap there.
 RUNWW_CASES = $(wildcard test/wcc/data/*/case.ww)
-test-run: all
+test-run: all | $(TESTS) test-lang test-lang-byteid
 	@BIN=$(BIN) $(BIN)/ww run test/runww.ww $(RUNWW_CASES)
 
 # ---- test-lang: in-language @test behavior corpus (fold 2) -------------