Add duplicate block filtering and chain-scoped deletion to chain import/export

- Add DISTINCT clause to block query in export_chain to prevent duplicate blocks in export
- Add chain_id filter to all delete operations in import_chain (blocks, accounts, transactions)
- Add commit after deletions before starting imports to ensure clean state
- Add duplicate block filtering by height before import to prevent UNIQUE constraint violations
- Add logging for deletion operations showing chain_id being cleared

apps/blockchain-node/src/aitbc_chain/rpc/router.py

@@ -678,8 +678,8 @@ async def export_chain(chain_id: str = None) -> Dict[str, Any]:
     try:
         # Use session_scope for database operations
         with session_scope() as session:
-            # Get all blocks
-            blocks_result = session.execute(select(Block).order_by(Block.height))
+            # Get all blocks - use DISTINCT to prevent duplicates
+            blocks_result = session.execute(select(Block).distinct().order_by(Block.height))
             blocks = list(blocks_result.scalars().all())
             
             # Get all accounts
@@ -775,13 +775,28 @@ async def import_chain(import_data: dict) -> Dict[str, Any]:
                 _logger.info(f"Backing up existing chain with {existing_count} blocks")
             
             # Clear existing data - only clear accounts if we have accounts to import
-            session.execute(delete(Block))
+            _logger.info(f"Clearing existing blocks for chain {chain_id}")
+            session.execute(delete(Block).where(Block.chain_id == chain_id))
             if accounts:
-                session.execute(delete(Account))
-            session.execute(delete(Transaction))
+                _logger.info(f"Clearing existing accounts for chain {chain_id}")
+                session.execute(delete(Account).where(Account.chain_id == chain_id))
+            _logger.info(f"Clearing existing transactions for chain {chain_id}")
+            session.execute(delete(Transaction).where(Transaction.chain_id == chain_id))
+            session.commit()  # Commit all deletes before imports
             
-            # Import blocks
+            # Import blocks - filter duplicates by height to avoid UNIQUE constraint violations
+            seen_heights = set()
+            unique_blocks = []
             for block_data in blocks:
+                if block_data["height"] not in seen_heights:
+                    seen_heights.add(block_data["height"])
+                    unique_blocks.append(block_data)
+                else:
+                    _logger.warning(f"Skipping duplicate block at height {block_data['height']}")
+            
+            _logger.info(f"Importing {len(unique_blocks)} unique blocks (filtered from {len(blocks)} total)")
+            
+            for block_data in unique_blocks:
                 block = Block(
                     chain_id=chain_id,
                     height=block_data["height"],
@@ -790,7 +805,8 @@ async def import_chain(import_data: dict) -> Dict[str, Any]:
                     proposer=block_data["proposer"],
                     timestamp=datetime.fromisoformat(block_data["timestamp"]) if block_data["timestamp"] else None,
                     state_root=block_data.get("state_root"),
-                    tx_count=block_data["tx_count"]
+                    tx_count=block_data["tx_count"],
+                    block_metadata=block_data.get("block_metadata")
                 )
                 session.add(block)