mod: Ext 2 — weighted/aggregate scoring (:score-at-least), 154/154

Report :signals ({:kind :weight}) project to signal(Id, 'kind', weight) facts;
condition (:score-at-least N) compiles to aggregate_all(sum(W), signal(Id,_,W),T),
T >= N. Low-confidence signals accumulate past a threshold via genuine Prolog
arithmetic aggregation. Default policy untouched — proven via custom rule sets.
+8 extension tests.

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

plans/mod-on-sx.md

@@ -16,7 +16,7 @@ federation extension.
 
 ## Status (rolling)
 
-`bash lib/mod/conformance.sh` → **146/146** (roadmap done + extensions in progress)
+`bash lib/mod/conformance.sh` → **154/154** (roadmap done + extensions in progress)
 
 ## Ground rules
 
@@ -137,12 +137,23 @@ lib/mod/fed.sx
   prefix `\+` operator). Closed-world example: "hide spam UNLESS author verified".
   Default policy untouched — demonstrated via custom rule sets, so all 132 base
   tests stay green.
-- [ ] Ext 2 — weighted/aggregate evidence scoring + threshold rules
+- [x] **Ext 2 — weighted/aggregate scoring** (+8). Report `:signals` ({:kind
+  :weight}) project to `signal(Id, 'kind', weight)` facts; condition
+  `(:score-at-least N)` → `aggregate_all(sum(W), signal(Id, _, W), T), T >= N`.
+  Many weak signals accumulate past a threshold — genuine Prolog arithmetic
+  aggregation. Default policy untouched.
 - [ ] Ext 3 — human-readable proof explanation (render a decision's `:goals`)
 - [ ] Ext 4 — report linking / dedup (relations between reports about one subject)
 
 ## Progress log
 
+- **Ext 2 — weighted/aggregate scoring, 154/154** (+8). `:signals` + the
+  `(:score-at-least N)` condition push aggregation into Prolog
+  (`aggregate_all(sum(W), …)`), so low-confidence signals can accumulate to a
+  takedown. The schema's report-rebuild helpers (`report*` / `with-*`) now thread
+  six fields; each addition stays non-breaking because empty collections project
+  to empty fact blocks. Default policy and its 132 tests untouched (proven via
+  custom rule sets).
 - **Ext 1 — negation-as-failure, 146/146** (+14). `:attr` and `:not` conditions
   give the policy closed-world reasoning. The substrate's negation is a functor
   (`not(Goal)`), not the ISO prefix `\+` operator (that doesn't parse here) —