ww: test sources are *_test.ww only (Go contract)

Go compiles only _test.go files as tests; discovery now keys on the
_test.ww suffix alone. The line-leading-@test compatibility allowance
(noncanonical filenames admitted as test sources) is removed from both
driver stages and the coordinator. An @test declaration outside a
*_test.ww file is rejected loudly ("@test declaration outside
*_test.ww", wording byte-identical cs/ww) instead of silently running
under compose or silently dropping in a non-T build (#6). Tree audit
found zero real carriers; the two allowance fixtures flip canonical
(dep_test.ww, widget_test.ww). New pins: direnum attest-noncanon
reject row (both-stage stderr parity) and the coordinator
noncanonical_attest_rejected package row.

test/package/dependency/dep/dep_test.ww

@@ -0,0 +1,7 @@
+package dep;
+
+// Go's contract: a package's *_test.ww sources are not part of the
+// imported package.  Must be excluded when dep is imported by root.
+@test fn imported_dependency_test_must_not_leak() void = {
+	assert(false);
+};

test/package/dependency/dep/deptest.ww

@@ -1,7 +0,0 @@
-package dep;
-
-// Noncanonical migration spelling: the actual line-leading @test makes this
-// test-only.  It must be excluded when dep is imported by the root package.
-@test fn imported_dependency_test_must_not_leak() void = {
-	assert(false);
-};

test/package/package_test.ww

@@ -232,6 +232,26 @@ fn packagepath(relative: str) str = {
 	clean(root);
 };
 
+// Go's contract: only *_test.ww sources are test sources; a line-leading
+// @test anywhere else fails classification loudly rather than run or
+// drop silently.
+@test fn noncanonical_attest_rejected() void = {
+	let root: str = fresh();
+	let pkgdir: str = strings.concat(root, "/noncanon");
+	assert(os.mkdir(pkgdir, 448i32) == 0);
+	writefile(strings.concat(pkgdir, "/noncanon.ww"), strings.concat(
+		"package noncanon;\n",
+		"@test fn hidden() void = { assert(false); };\n"));
+	let av: []str = [driver("ww"), "test", pkgdir];
+	let out: commandout;
+	runcommand(root, "noncanon", av,
+		(30i64 * (time.second: i64)): time.duration, &out);
+	expectexit(&out, 1);
+	assert(has(out.stderr, "@test declaration outside *_test.ww"));
+	assert(!has(out.stdout, "hidden"));
+	clean(root);
+};
+
 @test fn empty_and_invalid_package_classes() void = {
 	let root: str = fresh();
 	let av: []str = [driver("ww"), "test", packagepath("no_tests")];