datalog: cooking-posts canonical demo (Phase 10, 162/162)

Adds the canonical Phase 10 example from the plan: "Posts about
cooking by people I follow (transitively)." dl-demo-cooking-rules
defines reach over the follow graph (recursive transitive closure)
and cooking-post-by-network joining reach + authored + (tagged P
cooking). 3 new demo tests cover transitive network, direct-only
follow, and empty-network cases.

lib/datalog/demo.sx

@@ -64,6 +64,26 @@
      (subgroup-trans X Z <- (subgroup X Y) (subgroup-trans Y Z))
      (can-access A R <- (in-group A G) (allowed G R)))))
 
+;; ── Demo 4: cooking-posts (the canonical Phase 10 query) ────────
+;; "Posts about cooking by people I follow (transitively)."
+;; Combines federation (follows + transitive reach), authoring,
+;; tagging — the rose-ash multi-domain join.
+;;
+;; EDB:
+;;   (follows ACTOR-A ACTOR-B)
+;;   (authored ACTOR POST)
+;;   (tagged POST TAG)
+(define
+  dl-demo-cooking-rules
+  (quote
+    ((reach Me Them <- (follows Me Them))
+     (reach Me Them <- (follows Me X) (reach X Them))
+     (cooking-post-by-network Me P
+       <-
+       (reach Me Author)
+       (authored Author P)
+       (tagged P cooking)))))
+
 ;; ── Loader stub ──────────────────────────────────────────────────
 ;; Wiring to PostgreSQL would replace these helpers with calls into
 ;; rose-ash's internal HTTP RPC (fetch_data → /internal/data/...).

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 159,
+  "total_passed": 162,
   "total_failed": 0,
-  "total": 159,
+  "total": 162,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,7 +13,7 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":13,"failed":0,"total":13},
     {"name":"api","passed":9,"failed":0,"total":9},
-    {"name":"demo","passed":10,"failed":0,"total":10}
+    {"name":"demo","passed":13,"failed":0,"total":13}
   ],
-  "generated": "2026-05-08T09:02:31+00:00"
+  "generated": "2026-05-08T09:05:25+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**159 / 159 passing** (0 failure(s)).
+**162 / 162 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -13,4 +13,4 @@
 | negation | 10 | 10 | ok |
 | aggregates | 13 | 13 | ok |
 | api | 9 | 9 | ok |
-| demo | 10 | 10 | ok |
+| demo | 13 | 13 | ok |

lib/datalog/tests/demo.sx

@@ -179,6 +179,41 @@
           (quote (can-access X blog)))
         (list {:X (quote carol)}))
 
+      ;; ── Cooking posts (canonical Phase 10 example) ─────────
+      (dl-demo-test-set! "cooking posts by network"
+        (dl-query
+          (dl-demo-make
+            (quote
+              ((follows me alice) (follows alice bob) (follows alice carol)
+               (authored alice p1) (authored bob p2)
+               (authored carol p3) (authored carol p4)
+               (tagged p1 travel) (tagged p2 cooking)
+               (tagged p3 cooking) (tagged p4 books)))
+            dl-demo-cooking-rules)
+          (quote (cooking-post-by-network me P)))
+        (list {:P (quote p2)} {:P (quote p3)}))
+
+      (dl-demo-test-set! "cooking — direct follow only"
+        (dl-query
+          (dl-demo-make
+            (quote
+              ((follows me bob)
+               (authored bob p1) (authored bob p2)
+               (tagged p1 cooking) (tagged p2 books)))
+            dl-demo-cooking-rules)
+          (quote (cooking-post-by-network me P)))
+        (list {:P (quote p1)}))
+
+      (dl-demo-test-set! "cooking — none in network"
+        (dl-query
+          (dl-demo-make
+            (quote
+              ((follows me bob)
+               (authored bob p1) (tagged p1 books)))
+            dl-demo-cooking-rules)
+          (quote (cooking-post-by-network me P)))
+        (list))
+
       (dl-demo-test-set! "no access without grant"
         (dl-query
           (dl-demo-make