Fix checkpoint validation using wrong range limit

src/side_chain.cpp

@@ -3710,11 +3710,13 @@ bool SideChain::validate_loaded_checkpoints()
         for (const Checkpoint& cp : m_checkpoints) {
             LOGINFO(3, "Validating checkpoint at height " << cp.height);
 
-            // First check if checkpoint is reachable (within PPLNS window of current tip)
+            // First check if checkpoint is reachable (within checkpoint history range of current tip)
+            // Use CHECKPOINT_HISTORY * CHECKPOINT_INTERVAL, not m_chainWindowSize
             const PoolBlock* tip = m_chainTip;
-            if (tip && (cp.height + m_chainWindowSize < tip->m_sidechainHeight)) {
-                // Checkpoint is too old - outside sync window, discard it
-                LOGWARN(0, "Checkpoint at height " << cp.height << " is unreachable (tip=" << tip->m_sidechainHeight << ", window=" << m_chainWindowSize << ") - discarding stale checkpoint");
+            const uint64_t checkpoint_range = CHECKPOINT_HISTORY * CHECKPOINT_INTERVAL;
+            if (tip && (cp.height + checkpoint_range < tip->m_sidechainHeight)) {
+                // Checkpoint is too old - outside checkpoint history range, discard it
+                LOGINFO(2, "Checkpoint at height " << cp.height << " is outside history range (tip=" << tip->m_sidechainHeight << ", range=" << checkpoint_range << ") - discarding");
                 had_stale = true;
                 continue;  // Don't add to valid_checkpoints
             }