mod: Ext 17 — per-domain policy registry, 364/364

mod/register-policy! domain rules + mod/decide-in domain r reports give each
rose-ash domain its own rule set; unregistered domains fall back to default-rules
(never unmoderated). Same spam report → remove under a strict market policy, hide
under blog default. Engine already took rules as a param, so this is registry +
fallback, no engine change. +14 tests.

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

lib/mod/policies.sx

@@ -0,0 +1,40 @@
+;; lib/mod/policies.sx — per-domain policy registry.
+;;
+;; rose-ash spans domains (blog, market, events, federation, …) that want
+;; different moderation — a marketplace listing and a blog comment are not held to
+;; the same bar. This registry maps a domain to a rule set; mod/decide-in resolves
+;; the right policy and decides. Unregistered domains fall back to the default
+;; rules, so adding a domain never leaves it unmoderated.
+
+(define mod/*policies* (list))
+
+(define mod/policies-reset! (fn () (set! mod/*policies* (list))))
+
+(define
+  mod/register-policy!
+  (fn (domain rules) (begin (append! mod/*policies* {:domain domain :rules rules}) true)))
+
+(define
+  mod/policy-registered?
+  (fn
+    (domain)
+    (mod/any? (fn (p) (= (get p :domain) domain)) mod/*policies*)))
+
+(define
+  mod/policy-for
+  (fn
+    (domain)
+    (reduce
+      (fn (acc p) (if (= (get p :domain) domain) (get p :rules) acc))
+      mod/default-rules
+      mod/*policies*)))
+
+(define
+  mod/decide-in
+  (fn
+    (domain r reports)
+    (mod/decide-report r reports (mod/policy-for domain))))
+
+(define
+  mod/registered-domains
+  (fn () (map (fn (p) (get p :domain)) mod/*policies*)))