diff --git a/Makefile b/Makefile
index 9972a58a..7868f98e 100644
--- a/Makefile
+++ b/Makefile
@@ -109,6 +109,14 @@ CSTAGE_BINS	= $(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l $(BIN)/wwdump
 # (tests 990-994).
 WWSTAGE_BINS	= $(BIN)/wwdump_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww $(BIN)/ww_ww
 
+# Driver-produced binaries build in persistent per-target `ww build -w`
+# workdirs: package artifacts are reused across rebuilds on exact content
+# identity (see docs/test-system-v2.md), and the finished binary is
+# published into $(BIN) by one atomic mv. One workdir per target keeps
+# `make -jN` recipe concurrency race-free. test-incremental proves the
+# reuse path byte-identical to a from-scratch build.
+WWBUILD	= $(OUT)/wwbuild
+
 BINS	= $(CSTAGE_BINS) $(WWSTAGE_BINS) $(WWTEST_BIN)
 LIBS	= $(LIB)/libwcc.a $(LIB)/libwwrt.a
 
@@ -174,17 +182,12 @@ $(BIN)/wwdump_ww: selfhost/cmd/wwdump/main.ww \
 		lib/os/os.ww lib/rt/malloc.ww lib/time/time.ww lib/strconv/strconv.ww lib/strconv/stof_data.ww lib/strconv/decimal.ww lib/strconv/stof.ww lib/strconv/ftos_data.ww lib/strconv/ftos.ww lib/strings/strings.ww lib/bytes/bytes.ww lib/encoding/utf8/utf8.ww lib/ascii/ascii.ww lib/errors/errors.ww lib/io/io.ww lib/io/stream.ww lib/io/types.ww lib/memio/memio.ww lib/fmt/fmt.ww \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/wwdump_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/wwdump_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/lib/ww -I $(CURDIR)/selfhost/cmd/wcc \
-			$(CURDIR)/selfhost/cmd/wwdump/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/wwdump_ww
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/wwdump_ww \
+		-o $(WWBUILD)/wwdump_ww/main \
+		-I $(CURDIR)/lib/ww -I $(CURDIR)/selfhost/cmd/wcc \
+		$(CURDIR)/selfhost/cmd/wwdump/main.ww
+	@mv $(WWBUILD)/wwdump_ww/main $@
 
 # ---- ww-side w6c (compiler port, exercised by 994_w6c_ww) -------------
 # Thin driver: parse + cgen. The frontend (lex/parse/ast/...) is the
@@ -199,17 +202,12 @@ $(BIN)/w6c_ww: selfhost/cmd/w6c/main.ww \
 		lib/os/os.ww lib/rt/malloc.ww lib/time/time.ww lib/strconv/strconv.ww lib/strconv/stof_data.ww lib/strconv/decimal.ww lib/strconv/stof.ww lib/strconv/ftos_data.ww lib/strconv/ftos.ww lib/strings/strings.ww lib/bytes/bytes.ww lib/encoding/utf8/utf8.ww lib/ascii/ascii.ww lib/errors/errors.ww lib/io/io.ww lib/io/stream.ww lib/io/types.ww lib/memio/memio.ww lib/fmt/fmt.ww \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/w6c_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/w6c_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/lib/ww -I $(CURDIR)/selfhost/cmd/wcc \
-			$(CURDIR)/selfhost/cmd/w6c/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/w6c_ww
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/w6c_ww \
+		-o $(WWBUILD)/w6c_ww/main \
+		-I $(CURDIR)/lib/ww -I $(CURDIR)/selfhost/cmd/wcc \
+		$(CURDIR)/selfhost/cmd/w6c/main.ww
+	@mv $(WWBUILD)/w6c_ww/main $@
 
 # ---- ww-side w6a (assembler port, exercised by 991_w6a_ww) ------------
 # Built like wwdump_ww. Needs -I selfhost/cmd/w6a for the local types/lex/
@@ -221,17 +219,12 @@ $(BIN)/w6a_ww: selfhost/cmd/w6a/main.ww selfhost/cmd/w6a/opcodes.ww \
 		lib/strings/strings.ww lib/bytes/bytes.ww lib/encoding/utf8/utf8.ww \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/w6a_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/w6a_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/selfhost/cmd/w6a \
-			$(CURDIR)/selfhost/cmd/w6a/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/w6a_ww
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/w6a_ww \
+		-o $(WWBUILD)/w6a_ww/main \
+		-I $(CURDIR)/selfhost/cmd/w6a \
+		$(CURDIR)/selfhost/cmd/w6a/main.ww
+	@mv $(WWBUILD)/w6a_ww/main $@
 
 # ---- ww-side w6l (linker port, exercised by 992_w6l_ww) ---------------
 # Built like 6a_ww. Needs -I selfhost/cmd/w6l for the local sym/obj/pass/
@@ -244,17 +237,12 @@ $(BIN)/w6l_ww: selfhost/cmd/w6l/main.ww selfhost/cmd/w6l/sym.ww \
 		lib/strings/strings.ww lib/bytes/bytes.ww lib/encoding/utf8/utf8.ww \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/w6l_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/w6l_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/selfhost/cmd/w6l \
-			$(CURDIR)/selfhost/cmd/w6l/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/w6l_ww
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/w6l_ww \
+		-o $(WWBUILD)/w6l_ww/main \
+		-I $(CURDIR)/selfhost/cmd/w6l \
+		$(CURDIR)/selfhost/cmd/w6l/main.ww
+	@mv $(WWBUILD)/w6l_ww/main $@
 
 # ---- ww-side ww driver (exercised by 993_ww_ww) ------------------------
 # The driver pulls in lib/os (default search path) and orchestrates
@@ -265,16 +253,11 @@ $(BIN)/ww_ww: selfhost/cmd/ww/main.ww lib/os/exec/exec.ww \
 		lib/strings/strings.ww lib/bytes/bytes.ww lib/encoding/utf8/utf8.ww \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/ww_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/ww_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			$(CURDIR)/selfhost/cmd/ww/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/ww_ww
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/ww_ww \
+		-o $(WWBUILD)/ww_ww/main \
+		$(CURDIR)/selfhost/cmd/ww/main.ww
+	@mv $(WWBUILD)/ww_ww/main $@
 
 # ---- runtime (libwwrt.a, assembled by our own w6a) ---------------------
 $(OBJ)/rt/%.o: rt/%.s $(BIN)/w6a | $(OBJ)/rt
@@ -293,16 +276,11 @@ $(LIB)/libwwrt.a: $(RT_OBJ) | $(LIB)
 
 $(WWTEST_BIN): $(WWTEST_SRC) $(BIN)/ww $(BIN)/w6c $(BIN)/w6a \
 		$(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/wwtest.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/wwtest.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/internal $(CURDIR)/cmd/wwtest/wwtest.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/wwtest
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/wwtest \
+		-o $(WWBUILD)/wwtest/main \
+		-I $(CURDIR)/internal $(CURDIR)/cmd/wwtest/wwtest.ww
+	@mv $(WWBUILD)/wwtest/main $@
 
 wwfixture: $(WWFIXTURE_BIN)
 
@@ -314,54 +292,35 @@ test-wwfixture: wwfixture test-wwfixture-process
 	sh test/wwfixture/integration.sh
 
 $(WWFIXTURE_BIN): $(WWFIXTURE_SRC) $(WWFIXTURE_BUILD_TOOLS) | $(BIN)
-	@mkdir -p $(BIN)/wwfixture.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/wwfixture.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/internal $(CURDIR)/cmd/wwfixture/wwfixture.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/wwfixture
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/wwfixture \
+		-o $(WWBUILD)/wwfixture/main \
+		-I $(CURDIR)/internal $(CURDIR)/cmd/wwfixture/wwfixture.ww
+	@mv $(WWBUILD)/wwfixture/main $@
 
 $(EXEC_TEST_C): $(EXEC_TEST_SRC) $(WWFIXTURE_TOOLS) | $(BIN)
-	@mkdir -p $(BIN)/test_exec.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/test_exec.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww build -o main \
-			-I $(CURDIR)/internal $(CURDIR)/test/wwfixture/process/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/test_exec
+	@$(CURDIR)/$(BIN)/ww build -w $(WWBUILD)/test_exec \
+		-o $(WWBUILD)/test_exec/main \
+		-I $(CURDIR)/internal $(CURDIR)/test/wwfixture/process/main.ww
+	@mv $(WWBUILD)/test_exec/main $@
 
+# Built by the wwstage driver: the ordinary Make path exercises
+# ww_ww's -w implementation, not only the cstage twin's.
 $(EXEC_TEST_WW): $(EXEC_TEST_SRC) $(WWFIXTURE_TOOLS) | $(BIN)
-	@mkdir -p $(BIN)/test_exec_ww.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/test_exec_ww.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww_ww build -o main \
-			-I $(CURDIR)/internal $(CURDIR)/test/wwfixture/process/main.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/test_exec_ww
+	@$(CURDIR)/$(BIN)/ww_ww build -w $(WWBUILD)/test_exec_ww \
+		-o $(WWBUILD)/test_exec_ww/main \
+		-I $(CURDIR)/internal $(CURDIR)/test/wwfixture/process/main.ww
+	@mv $(WWBUILD)/test_exec_ww/main $@
 
 $(PACKAGE_TEST_BIN): $(PACKAGE_TEST_SRC) $(WWTEST_BIN) \
 		$(BIN)/ww $(BIN)/ww_ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
-	@mkdir -p $(BIN)/test_package.d
-	@d=$$(mktemp -d "$(CURDIR)/$(BIN)/test_package.d/build.XXXXXX") || exit 1; \
-		rc=0; published=0; \
-		(cd "$$d" && $(CURDIR)/$(BIN)/ww test -c -o main \
-			-I $(CURDIR)/internal $(CURDIR)/test/package/package_test.ww) || rc=$$?; \
-		rm -rf -- "$$d/main.sepwork" || { echo "$@: scratch cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; \
-		if [ $$rc -eq 0 ]; then mv "$$d/main" "$(CURDIR)/$@" && published=1 || rc=$$?; fi; \
-		if [ $$published -eq 0 ]; then rm -f -- "$$d/main" || { echo "$@: output cleanup failed" >&2; if [ $$rc -eq 0 ]; then rc=1; fi; }; fi; \
-		if ! rmdir "$$d"; then echo "$@: workspace cleanup failed" >&2; if [ $$published -eq 1 ]; then rm -f -- "$(CURDIR)/$@" || echo "$@: published-output cleanup failed" >&2; fi; if [ $$rc -eq 0 ]; then rc=1; fi; fi; \
-		exit $$rc
+	@mkdir -p $(WWBUILD)/test_package
+	@$(CURDIR)/$(BIN)/ww test -c -w $(WWBUILD)/test_package \
+		-I $(CURDIR)/internal $(CURDIR)/test/package/package_test.ww
+	@mv $(WWBUILD)/test_package/main $@
 
 test-package: all $(PACKAGE_TEST_BIN)
 	@WW_PACKAGE_REPO=$(CURDIR) $(CURDIR)/$(PACKAGE_TEST_BIN)