mod: Ext 1 — negation-as-failure conditions (:not / :attr), 146/146

Report attributes (:attrs) project to attr(Id, name) facts; policy gains (:attr x)
and (:not <cond>) conditions. The Prolog substrate exposes negation as a functor
not(Goal) (the prefix \+ operator doesn't parse here). Closed-world example:
hide spam unless author verified. Default policy untouched — feature proven via
custom rule sets, so all 132 base tests stay green. +14 extension tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/mod/policy.sx

@@ -42,6 +42,8 @@
 ;;
 ;; (:classification "spam") → classification(Id, spam)
 ;; (:evidence "kind")       → evidence(Id, 'kind', _)
+;; (:attr "verified")       → attr(Id, verified)
+;; (:not <cond>)            → not(<cond>)        (negation as failure)
 ;; (:count-at-least 3)      → report(Id, B, S), report_count(S, N), N >= 3
 
 (define
@@ -60,6 +62,9 @@
             ", "
             (mod/pl-quote (nth c 1))
             ", _)"))
+        ((= tag :attr) (str "attr(" idterm ", " (nth c 1) ")"))
+        ((= tag :not)
+          (str "not(" (mod/cond->goal (nth c 1) idterm) ")"))
         ((= tag :count-at-least)
           (str
             "report("