mod: Ext 7 — repeat-offender escalation (audit log as evidence), 223/223

mod/subject-sanctions counts prior hide/remove/ban decisions about a subject from
the append-only audit log; mod/decide-escalating upgrades a sanction to :ban when
the subject has >= k priors. Non-sanction outcomes (keep/escalate) pass through.
Closes the loop between audit and policy — the trail feeds future decisions. Own
suite. +19 tests.

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

lib/mod/tests/offenders.sx

@@ -0,0 +1,115 @@
+;; lib/mod/tests/offenders.sx — Ext 7: repeat-offender escalation.
+
+(define mod-off-count 0)
+(define mod-off-pass 0)
+(define mod-off-fail 0)
+(define mod-off-failures (list))
+
+(define
+  mod-off-test!
+  (fn
+    (name got expected)
+    (begin
+      (set! mod-off-count (+ mod-off-count 1))
+      (if
+        (= got expected)
+        (set! mod-off-pass (+ mod-off-pass 1))
+        (begin
+          (set! mod-off-fail (+ mod-off-fail 1))
+          (append!
+            mod-off-failures
+            (str name "\n    expected: " expected "\n    got:      " got)))))))
+
+;; ── sanction? predicate ──
+
+(mod-off-test! "hide is a sanction" (mod/sanction? "hide") true)
+(mod-off-test! "remove is a sanction" (mod/sanction? "remove") true)
+(mod-off-test! "ban is a sanction" (mod/sanction? "ban") true)
+(mod-off-test! "keep is not a sanction" (mod/sanction? "keep") false)
+(mod-off-test! "escalate is not a sanction" (mod/sanction? "escalate") false)
+
+;; ── repeat-offender escalation over the audit log ──
+
+(mod/reset!)
+(mod/report "u1" "spammer" "this is spam")
+(mod/report "u2" "spammer" "buy now offer")
+(mod/report "u3" "spammer" "click here free money")
+(mod/report "u4" "innocent" "fine post")
+
+(mod-off-test!
+  "no sanctions before any decision"
+  (mod/subject-sanctions "spammer")
+  0)
+
+(define mod-off-d1 (mod/decide-escalating "r1" 2))
+(mod-off-test!
+  "first spam → hide (0 priors)"
+  (get mod-off-d1 :action)
+  "hide")
+(mod-off-test!
+  "one sanction recorded"
+  (mod/subject-sanctions "spammer")
+  1)
+
+(define mod-off-d2 (mod/decide-escalating "r2" 2))
+(mod-off-test!
+  "second spam → hide (1 prior, below k=2)"
+  (get mod-off-d2 :action)
+  "hide")
+(mod-off-test!
+  "two sanctions recorded"
+  (mod/subject-sanctions "spammer")
+  2)
+
+(define mod-off-d3 (mod/decide-escalating "r3" 2))
+(mod-off-test!
+  "third spam → ban (2 priors ≥ k)"
+  (get mod-off-d3 :action)
+  "ban")
+(mod-off-test!
+  "ban decision names repeat-offender rule"
+  (get mod-off-d3 :rule)
+  "repeat-offender-ban")
+(mod-off-test!
+  "ban proof records prior sanction count"
+  (get (get mod-off-d3 :proof) :prior-sanctions)
+  2)
+
+;; ── different subjects accumulate independently ──
+
+(define mod-off-d4 (mod/decide-escalating "r4" 2))
+(mod-off-test!
+  "innocent keep → not escalated"
+  (get mod-off-d4 :action)
+  "keep")
+(mod-off-test!
+  "innocent has no sanctions"
+  (mod/subject-sanctions "innocent")
+  0)
+(mod-off-test!
+  "repeat-offender? true for spammer at k=2"
+  (mod/repeat-offender? "spammer" 2)
+  true)
+(mod-off-test!
+  "repeat-offender? false for innocent at k=1"
+  (mod/repeat-offender? "innocent" 1)
+  false)
+
+;; ── non-sanction decisions are never upgraded to ban ──
+;; r5 is a clean post, but it is the 4th report about "spammer", so the
+;; repeated-report rule escalates it. escalate is not a sanction, so it passes
+;; through decide-escalating unchanged (never becomes :ban).
+
+(mod/report "u5" "spammer" "a perfectly fine post")
+(define mod-off-d5 (mod/decide-escalating "r5" 1))
+(mod-off-test!
+  "non-sanction (escalate) decision is not upgraded to ban"
+  (get mod-off-d5 :action)
+  "escalate")
+
+(mod-off-test!
+  "decide-escalating unknown id → nil"
+  (mod/decide-escalating "r99" 2)
+  nil)
+
+(define mod-offenders-tests-run! (fn () {:failures mod-off-failures :total mod-off-count :passed mod-off-pass :failed mod-off-fail}))