datalog: comprehensive integration test (184/184)

Single program exercising recursion + stratified negation +
aggregation + comparison composed end-to-end via dl-eval. Confirms
the full pipeline (parser → safety → stratifier → semi-naive +
aggregate post-pass → query) on a non-trivial program.

  edge graph + banned set →
    reach transitive closure →
    safe (reach minus banned) →
    reach_count via count aggregation grouped by source →
    popular = reach_count >= 2

lib/datalog/tests/api.sx

@@ -213,6 +213,23 @@
           "?- p(X), q(X).")
         (list {:X 2} {:X 3}))
 
+      ;; Comprehensive integration: recursion + stratified negation
+      ;; + aggregation + comparison composed in a single program.
+      ;; (Uses _Anything as a regular var instead of `_` so the
+      ;;  outer rule binds via the reach lit.)
+      (dl-api-test-set! "integration"
+        (dl-eval
+          (str
+            "edge(a, b). edge(b, c). edge(c, d). edge(a, d). "
+            "banned(c). "
+            "reach(X, Y) :- edge(X, Y). "
+            "reach(X, Z) :- edge(X, Y), reach(Y, Z). "
+            "safe(X, Y) :- reach(X, Y), not(banned(Y)). "
+            "reach_count(X, N) :- reach(X, Z), count(N, Y, safe(X, Y)). "
+            "popular(X) :- reach_count(X, N), >=(N, 2).")
+          "?- popular(X).")
+        (list {:X (quote a)}))
+
       ;; dl-rule-from-list with no arrow → fact-style.
       (dl-api-test-set! "no arrow → fact-like rule"
         (let