feat(kernel): per-process budgets (pages, endpoints, notifs, regions) carved from creator, returned on death; init owns pool

crates/domain/src/budget_tests.rs

@@ -0,0 +1,35 @@
+use super::{Budget, Limits};
+
+const L: Limits = Limits {
+    pages: 10,
+    endpoints: 2,
+    notifications: 2,
+    regions: 1,
+};
+
+#[test]
+fn a_carve_takes_all_parts_or_none() {
+    let mut b = Budget::new(L);
+    b.endpoints.charge(2);
+    let child = Limits {
+        pages: 1,
+        endpoints: 1,
+        ..Limits::default()
+    };
+    assert!(!b.carve(child));
+    assert_eq!(b.limits(), L);
+    assert!(b.carve(Limits {
+        endpoints: 0,
+        ..child
+    }));
+    assert_eq!(b.limits().pages, 9);
+}
+
+#[test]
+fn a_refund_restores_what_was_carved() {
+    let mut b = Budget::new(L);
+    assert!(b.carve(L));
+    assert_eq!(b.limits(), Limits::default());
+    b.refund(L);
+    assert_eq!(b.limits(), L);
+}