fix: preserve first cross-node nonce owner

bounties/issue-2296/src/cross_node_replay_defense.py

@@ -302,14 +302,21 @@ def store_used_cross_node_nonce(
     expires_at = now_ts + CROSS_NODE_NONCE_TTL
 
     try:
-        conn.execute(
+        cleanup_expired_nonces(conn, now_ts)
+
+        cursor = conn.execute(
             """
-            INSERT OR REPLACE INTO cross_node_nonces 
+            INSERT OR IGNORE INTO cross_node_nonces
             (nonce, miner_id, node_id, first_seen, expires_at, attestation_hash, synced_at)
             VALUES (?, ?, ?, ?, ?, ?, ?)
             """,
             (nonce, miner_id, NODE_ID, now_ts, expires_at, attestation_hash, now_ts)
         )
+        if cursor.rowcount == 0:
+            conn.commit()
+            log.warning(f"Nonce {nonce[:16]}... already tracked; preserving original owner")
+            return False
+
         conn.commit()
 
         log.debug(f"Stored nonce {nonce[:16]}... for miner {miner_id}")

bounties/issue-2296/tests/test_cross_node_replay_defense.py

@@ -571,6 +571,53 @@ def test_miner_binding_invariant(self, test_db):
         assert valid is False
         assert error == "nonce_belongs_to_different_miner"
 
+    def test_store_preserves_first_active_nonce_owner(self, test_db):
+        """Storing an already-active nonce must not replace its first owner."""
+        nonce = "nonce_first_owner_invariant"
+
+        with patch('cross_node_replay_defense.NODE_ID', "node-original"):
+            first_result = store_used_cross_node_nonce(test_db, nonce, "miner_original")
+
+        with patch('cross_node_replay_defense.NODE_ID', "node-replay"):
+            second_result = store_used_cross_node_nonce(test_db, nonce, "miner_replay")
+
+        row = test_db.execute(
+            """
+            SELECT miner_id, node_id
+            FROM cross_node_nonces
+            WHERE nonce = ?
+            """,
+            (nonce,),
+        ).fetchone()
+
+        assert first_result is True
+        assert second_result is False
+        assert row == ("miner_original", "node-original")
+
+    def test_store_can_reuse_nonce_after_expiration(self, test_db):
+        """Expired records are cleaned before a fresh nonce owner is stored."""
+        nonce = "nonce_expired_then_reused"
+        past_time = 1700000000
+        future_time = past_time + CROSS_NODE_NONCE_TTL + 100
+
+        with patch('cross_node_replay_defense.NODE_ID', "node-old"):
+            store_used_cross_node_nonce(test_db, nonce, "miner_old", now_ts=past_time)
+
+        with patch('cross_node_replay_defense.NODE_ID', "node-new"):
+            result = store_used_cross_node_nonce(test_db, nonce, "miner_new", now_ts=future_time)
+
+        row = test_db.execute(
+            """
+            SELECT miner_id, node_id
+            FROM cross_node_nonces
+            WHERE nonce = ?
+            """,
+            (nonce,),
+        ).fetchone()
+
+        assert result is True
+        assert row == ("miner_new", "node-new")
+
 
 # =============================================================================
 # Regression Tests