diff --git a/contracts/risk_registry/src/lib.rs b/contracts/risk_registry/src/lib.rs
index a19af71..8cd81a5 100644
--- a/contracts/risk_registry/src/lib.rs
+++ b/contracts/risk_registry/src/lib.rs
@@ -2019,6 +2019,99 @@ mod tests {
             .is_ok());
     }
 
+    // ── add_verifier re-registration guard ───────────────────────────────────
+
+    #[test]
+    fn test_add_verifier_rejects_already_active_verifier() {
+        // Re-registering an active verifier must fail — previously this silently
+        // overwrote VerifierStake (stranding funds) and reset VerifierReputation.
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 2_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        let result = client.try_add_verifier(&admin, &verifier, &500_000i128);
+        assert!(result.is_err());
+        // Stake unchanged at original amount — no funds stranded
+        assert_eq!(client.get_verifier_stake(&verifier), 1_000_000i128);
+        assert!(client.is_verifier(&verifier));
+    }
+
+    #[test]
+    fn test_regression_fund_stranding_prevented() {
+        // Regression: second add_verifier with a lower amount must no longer
+        // silently overwrite VerifierStake, stranding the difference on-chain.
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 2_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        assert_eq!(client.get_verifier_stake(&verifier), 1_000_000i128);
+        // Attempt re-register with a lower stake — must be rejected
+        assert!(client.try_add_verifier(&admin, &verifier, &500_000i128).is_err());
+        // Tracked stake is still 1_000_000, not silently reduced to 500_000
+        assert_eq!(client.get_verifier_stake(&verifier), 1_000_000i128);
+    }
+
+    #[test]
+    fn test_regression_reputation_reset_prevented() {
+        // Regression: second add_verifier must not reset VerifierReputation to 100,
+        // laundering slashing history recorded via record_default.
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        let sme = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 2_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        client.register_sme(&verifier, &sme, &40u32, &true);
+        client.record_default(&admin, &sme);
+        let rep_after_slash = client.get_verifier_reputation(&verifier);
+        assert!(rep_after_slash < 100, "reputation should have been reduced");
+        // Attempt re-register — rejected, reputation preserved
+        let _ = client.try_add_verifier(&admin, &verifier, &1_000_000i128);
+        assert_eq!(client.get_verifier_reputation(&verifier), rep_after_slash);
+    }
+
+    #[test]
+    fn test_top_up_stake_increases_stake_additively() {
+        // top_up_stake must ADD to existing tracked stake, not overwrite it.
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 3_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        assert_eq!(client.get_verifier_stake(&verifier), 1_000_000i128);
+        client.top_up_stake(&admin, &verifier, &500_000i128);
+        assert_eq!(client.get_verifier_stake(&verifier), 1_500_000i128);
+    }
+
+    #[test]
+    fn test_top_up_stake_preserves_reputation() {
+        // top_up_stake must leave VerifierReputation untouched.
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        let sme = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 3_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        client.register_sme(&verifier, &sme, &40u32, &true);
+        client.record_default(&admin, &sme);
+        let rep = client.get_verifier_reputation(&verifier);
+        assert!(rep < 100);
+        client.top_up_stake(&admin, &verifier, &500_000i128);
+        assert_eq!(client.get_verifier_reputation(&verifier), rep);
+    }
+
+    #[test]
+    fn test_top_up_stake_requires_active_verifier() {
+        let (env, admin, _, staking_token, client) = setup();
+        let stranger = Address::generate(&env);
+        mint_stake(&env, &staking_token, &stranger, 1_000_000i128);
+        assert!(client.try_top_up_stake(&admin, &stranger, &500_000i128).is_err());
+    }
+
+    #[test]
+    fn test_top_up_stake_rejects_zero_amount() {
+        let (env, admin, _, staking_token, client) = setup();
+        let verifier = Address::generate(&env);
+        mint_stake(&env, &staking_token, &verifier, 1_000_000i128);
+        client.add_verifier(&admin, &verifier, &1_000_000i128);
+        assert!(client.try_top_up_stake(&admin, &verifier, &0i128).is_err());
     // ── set_credit_limit (require_non_negative_amount guard) ─────────────────
 
     #[test]