detect and break chain_recovery via step back

src/side_chain.cpp

@@ -3334,6 +3334,26 @@ void SideChain::trigger_recovery(uint64_t failure_height, uint64_t affected_main
         }
     }
 
+    // Detect recovery loops: if we're targeting the same checkpoint as last time,
+    // step back one more CHECKPOINT_INTERVAL to make actual progress.
+    const uint64_t last_recovery = m_lastRecoveryCheckpoint.load();
+    if (last_recovery > 0 && recovery_checkpoint >= last_recovery && recovery_checkpoint <= last_recovery + CHECKPOINT_INTERVAL) {
+        if (recovery_checkpoint >= CHECKPOINT_INTERVAL) {
+            LOGWARN(0, "Recovery loop detected: checkpoint " << recovery_checkpoint
+                    << " was already tried (last=" << last_recovery << ").");
+            recovery_checkpoint -= CHECKPOINT_INTERVAL;
+            LOGWARN(0, "Stepping back one more CHECKPOINT_INTERVAL to " << recovery_checkpoint);
+        } else {
+            LOGERR(0, "Recovery loop at checkpoint 0 - cannot go further back.");
+            LOGERR(0, "Stopping recovery; manual restart required.");
+            m_recoveryMode = false;
+            m_pendingRecoveryHeight = 0;
+            m_readyToMine = true;
+            return;
+        }
+    }
+    m_lastRecoveryCheckpoint = recovery_checkpoint;
+
     LOGINFO(0, "Recovery target checkpoint: " << recovery_checkpoint);
 
     m_pendingRecoveryHeight = recovery_checkpoint;

src/side_chain.h

@@ -249,6 +249,7 @@ private:
         std::atomic<bool> m_recoveryMode{false};
         std::atomic<uint64_t> m_pendingRecoveryHeight{0};
         bool m_checkpointsNeedValidation{false};
+        std::atomic<uint64_t> m_lastRecoveryCheckpoint{0};  // Detects and breaks recovery loops
 
         // Mainchain reorg tracking
         std::atomic<uint64_t> m_reorgGracePeriodEnd{0};