datalog: magic-sets rewriter (Phase 6, 202/202)

dl-magic-rewrite rules query-rel adn args returns:
  {:rules <rewritten-rules> :seed <magic-seed-fact>}

Worklist over (rel, adn) pairs starts from the query and stops
when no new pairs appear. For each rule with head matching a
worklist pair:
  - Adorned rule: head :- magic_<rel>^<adn>(bound), body...
  - Propagation rules: for each positive non-builtin body lit
    at position i:
      magic_<lit-rel>^<lit-adn>(bound-of-lit) :-
        magic_<rel>^<adn>(bound-of-head),
        body[0..i-1]
  - Add (lit-rel, lit-adn) to the worklist.

Built-ins, negation, and aggregates pass through without
generating propagation rules. EDB facts are unchanged.

3 new tests cover seed structure, equivalence on chain-3 (full
closure, 6 ancestor tuples — magic helps only when the EDB has
nodes outside the seed's transitive cone), and same-query-answers
under the rewritten program. Total 202/202.

Wiring up a `dl-saturate-magic!` driver and large-graph perf
benchmarks is left for a future iteration.

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 199,
+  "total_passed": 202,
   "total_failed": 0,
-  "total": 199,
+  "total": 202,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,8 +13,8 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":18,"failed":0,"total":18},
     {"name":"api","passed":14,"failed":0,"total":14},
-    {"name":"magic","passed":15,"failed":0,"total":15},
+    {"name":"magic","passed":18,"failed":0,"total":18},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T09:53:23+00:00"
+  "generated": "2026-05-08T09:58:16+00:00"
 }