relations: Phase 2 reachability + roots/leaves + cycles (engine.sx, kind-parameterized closure) + 24 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/relations/api.sx

@@ -1,25 +1,18 @@
-;; lib/relations/api.sx — relationship lifecycle + direct queries over lib/datalog/.
+;; lib/relations/api.sx — relationship lifecycle + queries over lib/datalog/.
 ;;
-;; A relations db is a live Datalog db holding rel(Src,Dst,Kind) facts. Phase 1
-;; uses no rules — direct children/parents are plain queries on the rel
-;; relation. Phase 2's engine.sx adds recursive reachability rules; build-db
-;; will fold them in then.
+;; A relations db is a live Datalog db holding rel(Src,Dst,Kind) facts under the
+;; engine ruleset (lib/relations/engine.sx). Direct children/parents are plain
+;; queries on the rel relation; transitive reachability/roots/leaves/cycles come
+;; from the engine's recursive rules.
 ;;
 ;; Two surfaces: db-threading core fns (relations-children-of db ...) and a
 ;; current-db convenience layer (relations/relate ...) for callers that load a
 ;; fact base once and query without passing the db around. This mirrors lib/acl.
 
-(define relations-rules (list))
-
 (define
   relations-build-db
   (fn (facts) (dl-program-data facts relations-rules)))
 
-;; Pull one column (by keyword key) out of a list of substitution dicts.
-(define
-  relations-pluck
-  (fn (substs key) (map (fn (s) (get s key)) substs)))
-
 ;; Direct children: every Dst with rel(node, Dst, kind).
 (define
   relations-children-of
@@ -94,3 +87,31 @@
 (define
   relations/related
   (fn (node kind) (relations-related (relations-ensure-db!) node kind)))
+
+(define
+  relations/descendants
+  (fn (node kind) (relations-descendants (relations-ensure-db!) node kind)))
+
+(define
+  relations/ancestors
+  (fn (node kind) (relations-ancestors (relations-ensure-db!) node kind)))
+
+(define
+  relations/reachable?
+  (fn (a b kind) (relations-reachable? (relations-ensure-db!) a b kind)))
+
+(define
+  relations/roots
+  (fn (kind) (relations-roots (relations-ensure-db!) kind)))
+
+(define
+  relations/leaves
+  (fn (kind) (relations-leaves (relations-ensure-db!) kind)))
+
+(define
+  relations/cycle?
+  (fn (node kind) (relations-cycle? (relations-ensure-db!) node kind)))
+
+(define
+  relations/acyclic?
+  (fn (kind) (relations-acyclic? (relations-ensure-db!) kind)))