brokerd: recall and memory, decided under built-in grants

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/brokerd/tests/grants.rs

@@ -92,7 +92,12 @@ fn files_that_do_not_end_in_toml_are_ignored() {
 fn an_empty_directory_is_a_valid_empty_set() {
     let set = load(&fixture("empty")).unwrap();
     assert!(set.grants().is_empty());
-    assert_eq!(set, GrantSet::default());
+    let builtin: Vec<&str> = set.matchable().map(|g| g.id.as_str()).collect();
+    assert_eq!(
+        builtin,
+        ["builtin-memory", "builtin-recall"],
+        "only the built-ins"
+    );
 }
 
 #[test]