diff --git a/cmd/ww/main.c b/cmd/ww/main.c
index f7102f22..45ce516e 100644
--- a/cmd/ww/main.c
+++ b/cmd/ww/main.c
@@ -1696,9 +1696,16 @@ do_test(int argc, char **argv)
 	size_t tlen = strlen(target);
 	if (strcmp(target, "...") == 0 ||
 	    (tlen >= 4 && strcmp(target + tlen - 4, "/...") == 0)) {
-		if (outstem[0]) {
+		if (emit_asm) {
 			fprintf(stderr,
-			    "ww test: -c/-S/-o need a single test file\n");
+			    "ww test: -S needs a single test file\n");
+			return 2;
+		}
+		/* -c -o forwards: the coordinator names the single
+		 * package's artifact and rejects a multi-package fan-out. */
+		if (outstem[0] && !compileonly) {
+			fprintf(stderr,
+			    "ww test: -o needs -c for a package target\n");
 			return 2;
 		}
 		if (workdir[0]) {
@@ -1725,9 +1732,14 @@ do_test(int argc, char **argv)
 			return 1;
 		}
 		if (is_dir) {
-			if (outstem[0]) {
+			if (emit_asm) {
 				fprintf(stderr,
-				    "ww test: -c/-S/-o need a single test file\n");
+				    "ww test: -S needs a single test file\n");
+				return 2;
+			}
+			if (outstem[0] && !compileonly) {
+				fprintf(stderr,
+				    "ww test: -o needs -c for a package target\n");
 				return 2;
 			}
 			if (workdir[0]) {
@@ -1862,8 +1874,12 @@ do_test(int argc, char **argv)
 		fprintf(stderr, "ww test: %s is neither file nor directory\n", target);
 		return 1;
 	}
-	if (outstem[0]) {
-		fprintf(stderr, "ww test: -c/-S/-o need a single test file\n");
+	if (emit_asm) {
+		fprintf(stderr, "ww test: -S needs a single test file\n");
+		return 2;
+	}
+	if (outstem[0] && !compileonly) {
+		fprintf(stderr, "ww test: -o needs -c for a package target\n");
 		return 2;
 	}
 	if (workdir[0]) {
diff --git a/docs/test-system-v2.md b/docs/test-system-v2.md
index 54b32bce..f9292769 100644
--- a/docs/test-system-v2.md
+++ b/docs/test-system-v2.md
@@ -207,9 +207,14 @@ at every `-j` level, and `-j 1` — the default — matches the former
 sequential loop exactly. Measured on the 31-package `lib/...` walk:
 7.0s sequential, 2.4s at `-j 4`. With `-c`, it publishes each exact
 `<package>.test` binary and adjacent `<package>.test.sepwork` tree in the
-package directory; those become caller-owned artifacts. Without `-c`, it
-removes the temporary binary and scratch with its workspace. The language
-runtime owns individual `@test` functions.
+package directory; those become caller-owned artifacts. `-c -o <name>`
+names that artifact instead of the fixed stem, for exactly one package:
+the coordinator rejects a multi-package fan-out ("cannot use -o with
+multiple packages", Go's `go test -o` rule), and `-o` without `-c` is
+rejected at the driver ("needs -c for a package target") because a plain
+run always executes from the temp root. Without `-c`, it removes the
+temporary binary and scratch with its workspace. The language runtime
+owns individual `@test` functions.
 
 Separate compilation is the only driver build path; no compatibility mode
 switch remains.
@@ -320,11 +325,8 @@ timeout policy in this architecture.
 
 ## Open driver work
 
-Carried over from the dissolved project plan; each is deliberate scope, not
-drift:
-
-- A package-level `-o` contract (single-file `ww test -o` exists; directory
-  packages publish fixed `<package>.test` stems under `-c`).
+None; the package-level `-o` contract (the last carried bullet) landed as
+`-c -o <name>` for exactly one package.
 
 ## Validation policy
 
diff --git a/internal/wwpackage/package.ww b/internal/wwpackage/package.ww
index 43aa40a2..b831ec8c 100644
--- a/internal/wwpackage/package.ww
+++ b/internal/wwpackage/package.ww
@@ -506,13 +506,17 @@ fn pkgcombined(g: *pkggroup, srcs: []pkgsource) bool = {
 };
 
 fn pkgsetpaths(g: *pkggroup, root: str, index: i32,
-	compileonly: bool) bool = {
+	compileonly: bool, outname: str) bool = {
 	let num: str = strconv.i32tos(index, strconv.base.DEC);
 	g.root = strings.concat(root, "/group-", num);
 	if (!pkgmakedir(g.root)) { return false; };
 	g.combined = strings.concat(g.root, "/package.ww");
 	if (compileonly) {
-		g.bin = strings.concat(g.dir, "/", g.pkg, ".test");
+		if (outname.len != 0) {
+			g.bin = outname;
+		} else {
+			g.bin = strings.concat(g.dir, "/", g.pkg, ".test");
+		};
 	} else {
 		g.bin = strings.concat(g.root, "/package.test");
 	};
@@ -669,6 +673,7 @@ export fn packagecommand(args: []str) int = {
 	let filters: []str = alloc([], (args.len + 1): u64)!;
 	let includes: []str = alloc([], (args.len + 1): u64)!;
 	let timeoutarg: str = "";
+	let outname: str = "";
 	let builder: str = pkgdefaultbuilder();
 	let i: i32 = 0;
 	for (i < args.len) {
@@ -688,6 +693,17 @@ export fn packagecommand(args: []str) int = {
 			i += 1;
 			continue;
 		};
+		if (strings.compare(a, "-o") == 0) {
+			if (i + 1 >= args.len) { pkgusage(); return 2; };
+			outname = args[i + 1];
+			i += 2;
+			continue;
+		};
+		if (strings.hasprefix(a, "-o") && a.len > 2) {
+			outname = a[2:a.len];
+			i += 1;
+			continue;
+		};
 		if (strings.hasprefix(a, "-timeout-ms=")) {
 			if (timeoutarg.len != 0 || a.len == 12
 				|| pkgparsedec(a[12:a.len], 3600000i64) <= 0i64) {
@@ -735,6 +751,12 @@ export fn packagecommand(args: []str) int = {
 		pkgusage();
 		return 2;
 	};
+	// -o names the -c artifact; a plain run always executes from the
+	// temp root, so a caller-owned name has nothing to name.
+	if (outname.len != 0 && !compileonly) {
+		pkgputln(os.STDERR_FILENO, "wwtest package: -o needs -c");
+		return 2;
+	};
 
 	// Go's ./... form: a trailing "..." path element walks the tree
 	// rooted at the prefix instead of one explicit directory.
@@ -870,6 +892,13 @@ export fn packagecommand(args: []str) int = {
 	};
 	if (groups.len == 0) { return 0; };
 	pkgsortgroups(groups);
+	// One caller-owned name cannot fan out (Go: `go test -o` with
+	// multiple packages is an error).
+	if (outname.len != 0 && groups.len > 1) {
+		pkgputln(os.STDERR_FILENO,
+			"wwtest package: cannot use -o with multiple packages");
+		return 2;
+	};
 
 	let borrowed: str = temp.dir();
 	let tmproot: str = strings.dup(borrowed);
@@ -894,7 +923,8 @@ export fn packagecommand(args: []str) int = {
 	for (emitted < groups.len) {
 		for (!stopped && launched < groups.len && active < jobs) {
 			let g: *pkggroup = &groups[launched];
-			if (!pkgsetpaths(g, tmproot, launched, compileonly)) {
+			if (!pkgsetpaths(g, tmproot, launched, compileonly,
+				outname)) {
 				g.fail = PKGFAILSETUP;
 				g.state = PKGDONE;
 				stopped = true;
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index 57772a6d..4685780a 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -2684,8 +2684,14 @@ fn dotest(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 			&& target[tlen - 1u64] == '.';
 	};
 	if (istree) {
-		if (outstem != nil) {
-			cerr("ww test: -c/-S/-o need a single test file\n");
+		if (emitasm != 0) {
+			cerr("ww test: -S needs a single test file\n");
+			return 2;
+		};
+		// -c -o forwards: the coordinator names the single
+		// package's artifact and rejects a multi-package fan-out.
+		if (outstem != nil && compileonly == 0) {
+			cerr("ww test: -o needs -c for a package target\n");
 			return 2;
 		};
 		if (workdir != nil) {
@@ -2728,8 +2734,12 @@ fn dotest(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 			emitasm, outstem, workdir, patarg);
 	};
 
-	if (outstem != nil) {
-		cerr("ww test: -c/-S/-o need a single test file\n");
+	if (emitasm != 0) {
+		cerr("ww test: -S needs a single test file\n");
+		return 2;
+	};
+	if (outstem != nil && compileonly == 0) {
+		cerr("ww test: -o needs -c for a package target\n");
 		return 2;
 	};
 	if (workdir != nil) {
diff --git a/test/package/package_test.ww b/test/package/package_test.ww
index 7cd417da..649a960c 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -569,7 +569,8 @@ fn packagepath(relative: str) str = {
 	expectexit(&outc, 2);
 	expectexit(&outw, 2);
 	assert(same(outc.stderr, outw.stderr));
-	assert(has(outc.stderr, "ww test: -c/-S/-o need a single test file\n"));
+	assert(has(outc.stderr,
+		"ww test: -o needs -c for a package target\n"));
 
 	let wdc: []str = [driver("ww"), "test", "-w", root, spec];
 	let wdw: []str = [driver("ww_ww"), "test", "-w", root, spec];
@@ -775,3 +776,72 @@ fn runtimepath(relative: str) str = {
 		"escaped_writer_does_not_hold_runner ... ok\n"));
 	clean(root);
 };
+
+// The package-level -o contract: -c -o names the single package's
+// artifact in place of the fixed <package>.test stem; -o without -c
+// has nothing to name (runs execute from the temp root); one name
+// cannot fan out over multiple packages (Go's `go test -o` rule).
+@test fn compile_artifact_naming() void = {
+	let root: str = fresh();
+	let pdir: str = strings.concat(root, "/pkg");
+	assert(os.mkdir(pdir, 493i32) == 0);
+	writefile(strings.concat(pdir, "/pkg.ww"),
+		"package pkg;\nexport fn v() i32 = { return 7; };\n");
+	writefile(strings.concat(pdir, "/pkg_test.ww"), strings.concat(
+		"package pkg_test;\nimport pkg;\n",
+		"@test fn seven() void = { assert(pkg.v() == 7); };\n"));
+	let adir: str = strings.concat(root, "/a");
+	assert(os.mkdir(adir, 493i32) == 0);
+	// '_'-prefixed: the tree walk skips it, so the artifacts and
+	// their .sepwork trees never pollute the multi-package discovery.
+	let outdir: str = strings.concat(root, "/_out");
+	assert(os.mkdir(outdir, 493i32) == 0);
+	writefile(strings.concat(adir, "/a.ww"),
+		"package a;\nexport fn v() i32 = { return 1; };\n");
+	writefile(strings.concat(adir, "/a_test.ww"), strings.concat(
+		"package a_test;\nimport a;\n",
+		"@test fn one() void = { assert(a.v() == 1); };\n"));
+	let out: commandout;
+	let drvs: []str = ["ww", "ww_ww"];
+	let i: i32 = 0;
+	for (i < 2) {
+		let named: str = strings.concat(outdir, "/out_", drvs[i],
+			".bin");
+		let coav: []str = [driver(drvs[i]), "test", "-c", "-o",
+			named, pdir];
+		runcommand(root, strings.concat("nameco_", drvs[i]), coav,
+			(30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		let fi: os.filestat;
+		match (os.stat(&fi, named)) {
+		case void => void;
+		case let e: os.oserror => abort("-c -o artifact missing");
+		};
+		match (os.stat(&fi, strings.concat(pdir, "/pkg.test"))) {
+		case void => abort("-c -o still published the fixed stem");
+		case let e: os.oserror => void;
+		};
+		let runav: []str = [named];
+		runcommand(root, strings.concat("namerun_", drvs[i]), runav,
+			(30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(has(out.stdout, "seven ... ok"));
+
+		let nocav: []str = [driver(drvs[i]), "test", "-o", named,
+			pdir];
+		runcommand(root, strings.concat("noc_", drvs[i]), nocav,
+			(30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 2);
+		assert(has(out.stderr, "-o needs -c for a package target"));
+
+		let mulav: []str = [driver(drvs[i]), "test", "-c", "-o",
+			named, strings.concat(root, "/...")];
+		runcommand(root, strings.concat("multi_", drvs[i]), mulav,
+			(30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 2);
+		assert(has(out.stderr,
+			"cannot use -o with multiple packages"));
+		i += 1;
+	};
+	clean(root);
+};