wwtest: native package-test coordinator

Single-directory package-test planner: discovers *.ww, groups white-box
and external <pkg>_test sources, composes the combined test package,
builds it through the sibling ww driver, and runs it with the runtime's
-package/-list/-timeout-ms contract. test/package holds its E2E corpus
and the manual runtime fixture set.

test/package/cases/descendant/descendant_test.ww

@@ -0,0 +1,25 @@
+package descendant_test;
+
+import os;
+
+@test fn normal_return_clears_descendant() void = {
+	let ready: [2]i32;
+	assert(os.pipe(&ready) == 0);
+	let pid: i32 = os.fork();
+	assert(pid >= 0);
+	if (pid == 0) {
+		os.close(ready[0]);
+		let mask: u64 = 1u64 << ((os.SIGTERM - 1): u64);
+		if (os.sigprocmask(os.SIG_BLOCK, &mask, nil: *u64) != 0) {
+			os.exit(120);
+		};
+		let b: [1]u8 = [1u8];
+		if (os.write(ready[1], &b[0], 1u64) != 1i64) { os.exit(121); };
+		os.close(ready[1]);
+		for (true) { };
+	};
+	os.close(ready[1]);
+	let b: [1]u8;
+	assert(os.read(ready[0], &b[0], 1u64) == 1i64);
+	os.close(ready[0]);
+};