feat(init): spawn service over IPC with per-client allowance refunded on child death; up to 4 death watchers; spawntest on test image

crates/kernel/src/tests/events.rs

@@ -161,3 +161,21 @@ fn notification_id(
         _ => panic!("not a notification"),
     }
 }
+
+#[test]
+fn every_watcher_hears_and_there_is_room_for_a_few() {
+    let (mut k, init, proc_cap, first) = watching();
+    let second = k.create_notification_cap(init).unwrap();
+    k.watch_death(init, proc_cap, second).unwrap();
+    // The same notification again takes no new place.
+    k.watch_death(init, proc_cap, second).unwrap();
+    for _ in 2..domain::timer::MAX_WATCHERS {
+        let n = k.create_notification_cap(init).unwrap();
+        k.watch_death(init, proc_cap, n).unwrap();
+    }
+    let extra = k.create_notification_cap(init).unwrap();
+    assert!(k.watch_death(init, proc_cap, extra).is_err());
+    k.handle_syscall(Syscall::Kill { process: proc_cap });
+    assert_eq!(k.poll(init, first).unwrap(), 1);
+    assert_eq!(k.poll(init, second).unwrap(), 1);
+}