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

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