mod: Ext 4 — report linking + dedup (Prolog-backed retrieval), 176/176

mod/related-ids and mod/reporters-of find reports about a subject via a Prolog
relational query (report(Id, _, 'subject')) — the policy substrate reused for
retrieval. mod/dedup-reports collapses identical reports by a normalized
reporter|subject|reason key; mod/distinct-reporters-of counts unique reporters.
Own suite (tests/link.sx). +12 tests.

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

lib/mod/tests/link.sx

@@ -0,0 +1,86 @@
+;; lib/mod/tests/link.sx — Ext 4: report linking + dedup.
+
+(define mod-lnk-count 0)
+(define mod-lnk-pass 0)
+(define mod-lnk-fail 0)
+(define mod-lnk-failures (list))
+
+(define
+  mod-lnk-test!
+  (fn
+    (name got expected)
+    (begin
+      (set! mod-lnk-count (+ mod-lnk-count 1))
+      (if
+        (= got expected)
+        (set! mod-lnk-pass (+ mod-lnk-pass 1))
+        (begin
+          (set! mod-lnk-fail (+ mod-lnk-fail 1))
+          (append!
+            mod-lnk-failures
+            (str name "\n    expected: " expected "\n    got:      " got)))))))
+
+;; ── link-key + dedup ──
+
+(define mod-lnk-a (mod/mk-report "r1" "alice" "bob" "this is spam"))
+(define mod-lnk-a2 (mod/mk-report "r2" "alice" "bob" "THIS IS SPAM"))
+(define mod-lnk-b (mod/mk-report "r3" "carol" "bob" "abuse"))
+(define mod-lnk-c (mod/mk-report "r4" "alice" "eve" "this is spam"))
+
+(mod-lnk-test!
+  "identical reports share a link key (case-insensitive reason)"
+  (= (mod/link-key mod-lnk-a) (mod/link-key mod-lnk-a2))
+  true)
+(mod-lnk-test!
+  "different reporter → different key"
+  (= (mod/link-key mod-lnk-a) (mod/link-key mod-lnk-b))
+  false)
+(mod-lnk-test!
+  "different subject → different key"
+  (= (mod/link-key mod-lnk-a) (mod/link-key mod-lnk-c))
+  false)
+
+(define mod-lnk-set (list mod-lnk-a mod-lnk-a2 mod-lnk-b mod-lnk-c))
+(mod-lnk-test!
+  "dedup collapses identical reports"
+  (len (mod/dedup-reports mod-lnk-set))
+  3)
+(mod-lnk-test!
+  "duplicate-count counts collapsed"
+  (mod/duplicate-count mod-lnk-set)
+  1)
+(mod-lnk-test!
+  "dedup of all-distinct keeps all"
+  (len (mod/dedup-reports (list mod-lnk-a mod-lnk-b mod-lnk-c)))
+  3)
+
+;; ── Prolog-backed relational linking ──
+
+(mod-lnk-test!
+  "related-ids finds all reports about subject"
+  (len (mod/related-ids "bob" mod-lnk-set))
+  3)
+(mod-lnk-test!
+  "related-ids returns the ids"
+  (mod/related-ids "eve" mod-lnk-set)
+  (list "r4"))
+(mod-lnk-test!
+  "related-ids empty for unknown subject"
+  (mod/related-ids "nobody" mod-lnk-set)
+  (list))
+
+;; reporters: bob reported by alice (x2) + carol → 3 raw, 2 distinct
+(mod-lnk-test!
+  "reporters-of counts all reports"
+  (len (mod/reporters-of "bob" mod-lnk-set))
+  3)
+(mod-lnk-test!
+  "distinct reporters-of dedups reporters"
+  (len (mod/distinct-reporters-of "bob" mod-lnk-set))
+  2)
+(mod-lnk-test!
+  "distinct utility removes dups"
+  (mod/distinct (list "a" "b" "a" "c" "b"))
+  (list "a" "b" "c"))
+
+(define mod-link-tests-run! (fn () {:failures mod-lnk-failures :total mod-lnk-count :passed mod-lnk-pass :failed mod-lnk-fail}))