From 5338975eea1c700de0cfb57f2892ac4e6895a6a3 Mon Sep 17 00:00:00 2001
From: Simon Axelsson <simon@siax.io>
Date: Mon, 7 Sep 2026 17:57:23 +0200
Subject: [PATCH] fix: make conflicting company identifiers dominate ER matches

---
 app/api/0pt/internal/er/candidates/route.ts | 34 ++++++++++++---------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/app/api/0pt/internal/er/candidates/route.ts b/app/api/0pt/internal/er/candidates/route.ts
index f03206b..8152aba 100644
--- a/app/api/0pt/internal/er/candidates/route.ts
+++ b/app/api/0pt/internal/er/candidates/route.ts
@@ -11,23 +11,27 @@ import { SiaxError } from "@/src/platform/errors";
 
 const er = new EntityResolutionService();
 
+/**
+ * Company identity hard rule.
+ *
+ * Negative identity evidence dominates positive evidence: if two records both
+ * carry the same identifier type and the values conflict, they MUST NOT be
+ * merged even if another identifier happens to match. Only when every shared
+ * stable identifier agrees may one matching identifier force a match.
+ */
 er.registerHardRule({
-  rule_id: "0pt.company.lei.v1",
+  rule_id: "0pt.company.stable-identifiers.v2",
   decide(a, b) {
-    const av = stringField(a, "lei");
-    const bv = stringField(b, "lei");
-    if (!av || !bv) return "abstain";
-    return av === bv ? "force_match" : "force_non_match";
-  },
-});
-
-er.registerHardRule({
-  rule_id: "0pt.company.org_nr.v1",
-  decide(a, b) {
-    const av = stringField(a, "org_nr");
-    const bv = stringField(b, "org_nr");
-    if (!av || !bv) return "abstain";
-    return av === bv ? "force_match" : "force_non_match";
+    const fields = ["lei", "org_nr"] as const;
+    let sharedMatch = false;
+    for (const field of fields) {
+      const av = stringField(a, field);
+      const bv = stringField(b, field);
+      if (!av || !bv) continue;
+      if (av !== bv) return "force_non_match";
+      sharedMatch = true;
+    }
+    return sharedMatch ? "force_match" : "abstain";
   },
 });