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/runtime/escaped_descendant_test.ww

@@ -0,0 +1,26 @@
+package runtime_escaped_descendant_test;
+
+import os;
+import time;
+
+@test fn escaped_writer_does_not_hold_runner() void = {
+	let fds: [2]i32;
+	assert(os.pipe(&fds) == 0);
+	let pid: i32 = os.fork();
+	assert(pid >= 0);
+	if (pid == 0) {
+		os.close(fds[0]);
+		if (os.setpgid(0, 0) != 0) { os.exit(120); };
+		let ready: u8 = 1u8;
+		if (os.write(fds[1], &ready, 1u64) != 1i64) { os.exit(121); };
+		os.close(fds[1]);
+		time.sleep((time.second: i64): time.duration,
+		    time.clock.monotonic);
+		os.exit(0);
+	};
+	os.close(fds[1]);
+	let ready: u8 = 0u8;
+	assert(os.read(fds[0], &ready, 1u64) == 1i64);
+	os.close(fds[0]);
+	assert(ready == 1u8);
+};