datalog: stratifier rejects recursion through aggregation (165/165)

Bug: dl-check-stratifiable iterated body literals looking only for
explicit :neg literals, missing aggregate cycles. Now also walks
aggregates via dl-aggregate-dep-edge — q(N) :- count(N, X, q(X))
correctly errors out at saturation time.

3 new tests cover:
- recursion-through-aggregation rejected
- negation + aggregation coexist when in different strata
- min over empty derived relation produces no result

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 162,
+  "total_passed": 165,
   "total_failed": 0,
-  "total": 162,
+  "total": 165,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -11,9 +11,9 @@
     {"name":"builtins","passed":19,"failed":0,"total":19},
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
-    {"name":"aggregates","passed":13,"failed":0,"total":13},
+    {"name":"aggregates","passed":16,"failed":0,"total":16},
     {"name":"api","passed":9,"failed":0,"total":9},
     {"name":"demo","passed":13,"failed":0,"total":13}
   ],
-  "generated": "2026-05-08T09:05:25+00:00"
+  "generated": "2026-05-08T09:12:57+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**162 / 162 passing** (0 failure(s)).
+**165 / 165 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -11,6 +11,6 @@
 | builtins | 19 | 19 | ok |
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |
-| aggregates | 13 | 13 | ok |
+| aggregates | 16 | 16 | ok |
 | api | 9 | 9 | ok |
 | demo | 13 | 13 | ok |

lib/datalog/strata.sx

@@ -197,18 +197,33 @@
                   (for-each
                     (fn
                       (lit)
-                      (when
+                      (cond
-                        (and (dict? lit) (has-key? lit :neg))
+                        ((and (dict? lit) (has-key? lit :neg))
-                        (let ((tgt (dl-rel-name (get lit :neg))))
+                          (let ((tgt (dl-rel-name (get lit :neg))))
-                          (when
+                            (when
-                            (and (not (nil? tgt))
+                              (and (not (nil? tgt))
-                                 (dl-reach-cycle? reach head-rel tgt))
+                                   (dl-reach-cycle? reach head-rel tgt))
-                            (set!
+                              (set!
-                              err
+                                err
-                              (str "non-stratifiable: relation " head-rel
+                                (str "non-stratifiable: relation " head-rel
-                                   " transitively depends through negation on "
+                                     " transitively depends through negation on "
-                                   tgt
+                                     tgt
-                                   " which depends back on " head-rel))))))
+                                     " which depends back on " head-rel)))))
+                        ((dl-aggregate? lit)
+                          (let ((edge (dl-aggregate-dep-edge lit)))
+                            (when
+                              (not (nil? edge))
+                              (let ((tgt (get edge :rel)))
+                                (when
+                                  (and (not (nil? tgt))
+                                       (dl-reach-cycle? reach head-rel tgt))
+                                  (set!
+                                    err
+                                    (str "non-stratifiable: relation "
+                                         head-rel
+                                         " aggregates over " tgt
+                                         " which depends back on "
+                                         head-rel))))))))) 
                     (get rule :body)))))
             (dl-rules db))
           err)))))

lib/datalog/tests/aggregates.sx

@@ -227,6 +227,39 @@
         (list {:L (list)}))
 
       ;; Aggregate vs single distinct.
+      ;; Stratification: recursion through aggregation is rejected.
+      (dl-at-test! "agg recursion rejected"
+        (dl-at-throws?
+          (fn ()
+            (let ((db (dl-make-db)))
+              (do
+                (dl-add-rule! db
+                  {:head (list (quote q) (quote N))
+                   :body (list (list (quote count) (quote N) (quote X)
+                                     (list (quote q) (quote X))))})
+                (dl-saturate! db)))))
+        true)
+
+      ;; Negation + aggregation in the same body — different strata.
+      (dl-at-test-set! "neg + agg coexist"
+        (dl-query
+          (dl-program
+            "u(a). u(b). u(c). banned(b).
+             active(X) :- u(X), not(banned(X)).
+             cnt(N) :- count(N, X, active(X)).")
+          (list (quote cnt) (quote N)))
+        (list {:N 2}))
+
+      ;; Min over a derived empty relation: no result.
+      (dl-at-test-set! "min over empty derived"
+        (dl-query
+          (dl-program
+            "s(50). s(60).
+             score(N) :- s(N), >(N, 100).
+             low(M) :- min(M, X, score(X)).")
+          (list (quote low) (quote M)))
+        (list))
+
       (dl-at-test-set! "distinct counted once"
         (dl-query
           (dl-program

plans/datalog-on-sx.md

@@ -273,6 +273,16 @@ large graphs.
 
 _Newest first._
 
+- 2026-05-08 — Bug fix: `dl-check-stratifiable` now rejects recursion
+  through aggregation (e.g., `q(N) :- count(N, X, q(X))`). The
+  stratifier was already adding negation-like edges for aggregates,
+  but the cycle scan only looked at explicit `:neg` literals. Added
+  the matching aggregate branch to the body iteration. Also adds
+  doc-only `lib/datalog/datalog.sx` with the public-API surface
+  (since `load` is an epoch command and can't recurse from within an
+  `.sx` file). 3 new aggregate tests cover recursion-rejection,
+  negation-and-aggregation coexistence, and min-over-empty-derived.
+
 - 2026-05-08 — Phase 10 demo + canonical query. Added the "cooking
   posts by people I follow (transitively)" example from the plan:
   `dl-demo-cooking-rules` defines `reach` over the follow graph