mod: Ext 8 — quorum over distinct reporters (anti-brigade), 232/232

(:reporters-at-least N) compiles to setof(Br, report(_, Br, Sr), Bsr),
length(Bsr, Nr), Nr >= N — counts distinct reporters, not raw reports.
mod/decide-quorum asserts every report's report/3 fact (base engine scopes to the
decided report) so Prolog can aggregate reporters. One user filing 3 reports stays
:keep under quorum while the count rule escalates. Own suite. +9 tests.

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

lib/mod/policy.sx

@@ -40,12 +40,15 @@
 
 ;; ── condition → Prolog goal ──
 ;;
-;; (: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
-;; (:score-at-least 5)      → aggregate_all(sum(W), signal(Id, _, W), T), T >= 5
+;; (: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
+;; (:score-at-least 5)       → aggregate_all(sum(W), signal(Id, _, W), T), T >= 5
+;; (:reporters-at-least 2)   → report(Id, _, Sr), setof(Br, report(_, Br, Sr), Bsr),
+;;                             length(Bsr, Nr), Nr >= 2   (distinct reporters;
+;;                             needs the quorum engine which asserts every report)
 
 (define
   mod/cond->goal
@@ -78,6 +81,13 @@
             idterm
             ", _, W), T), T >= "
             (nth c 1)))
+        ((= tag :reporters-at-least)
+          (str
+            "report("
+            idterm
+            ", _, Sr), setof(Br, report(_, Br, Sr), Bsr), "
+            "length(Bsr, Nr), Nr >= "
+            (nth c 1)))
         (true "true")))))
 
 (define