fix: Submit votes to ALL validators instead of single validator

Problem: Votes were only being submitted to one validator selected via
round-robin, then expected inter-validator broadcasting to propagate the
transaction. But inter-validator transaction broadcasting wasn't working
reliably.

Solution: Submit each vote to ALL healthy validators simultaneously.
This ensures every validator receives the transaction directly, making it
available for block creation regardless of inter-validator communication.

Benefits:
- No dependency on P2P transaction broadcasting
- All validators have same pending transaction pool
- Any validator can create blocks with all pending transactions
- More robust and simpler than trying to maintain P2P mesh

Implementation:
- Modified submit_vote() to loop through all healthy_validators
- Submit same JSON-RPC request to each validator
- Log results from each submission
- Require at least one successful submission

This is simpler and more reliable than the previous architecture.

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

e-voting-system/backend/blockchain_client.py

@@ -160,7 +160,10 @@ class BlockchainClient:
         ballot_hash: Optional[str] = None
     ) -> Dict[str, Any]:
         """
-        Submit a vote to the PoA blockchain network.
+        Submit a vote to ALL PoA validators simultaneously.
+
+        This ensures every validator receives the transaction directly,
+        guaranteeing it will be included in the next block.
 
         Args:
             voter_id: Voter identifier
@@ -178,13 +181,10 @@ class BlockchainClient:
         logger.info(f"[BlockchainClient.submit_vote] CALLED with voter_id={voter_id}, election_id={election_id}")
         logger.info(f"[BlockchainClient.submit_vote] healthy_validators count: {len(self.healthy_validators)}")
 
-        validator = self._get_healthy_validator()
-        if not validator:
+        if not self.healthy_validators:
             logger.error("[BlockchainClient.submit_vote] No healthy validators available!")
             raise Exception("No healthy validators available")
 
-        logger.info(f"[BlockchainClient.submit_vote] Selected validator: {validator.node_id}")
-
         # Generate transaction ID if not provided
         if not transaction_id:
             import uuid
@@ -224,21 +224,23 @@ class BlockchainClient:
             "id": transaction_id
         }
 
-        logger.info(f"[BlockchainClient.submit_vote] Submitting vote to {validator.node_id}: tx_id={transaction_id}")
-        logger.info(f"[BlockchainClient.submit_vote] RPC URL: {validator.rpc_url}/rpc")
+        # Submit to ALL healthy validators simultaneously
+        logger.info(f"[BlockchainClient.submit_vote] Submitting to {len(self.healthy_validators)} validators")
 
-        try:
+        results = {}
         if not self._client:
             logger.error("[BlockchainClient.submit_vote] AsyncClient not initialized!")
             raise Exception("AsyncClient not initialized")
 
-            logger.info(f"[BlockchainClient.submit_vote] Sending POST request to {validator.rpc_url}/rpc")
+        for validator in self.healthy_validators:
+            try:
+                logger.info(f"[BlockchainClient.submit_vote] Submitting to {validator.node_id} ({validator.rpc_url}/rpc)")
                 response = await self._client.post(
                     f"{validator.rpc_url}/rpc",
                     json=rpc_request,
                     timeout=self.timeout
                 )
-            logger.info(f"[BlockchainClient.submit_vote] Response received: status={response.status_code}")
+                logger.info(f"[BlockchainClient.submit_vote] Response from {validator.node_id}: status={response.status_code}")
 
                 response.raise_for_status()
                 result = response.json()
@@ -246,20 +248,28 @@ class BlockchainClient:
                 # Check for JSON-RPC errors
                 if "error" in result:
                     logger.error(f"RPC error from {validator.node_id}: {result['error']}")
-                raise Exception(f"RPC error: {result['error']}")
-
-            logger.info(f"✓ Vote submitted successfully: {transaction_id}")
-
-            return {
-                "transaction_id": transaction_id,
-                "block_hash": result.get("result"),
-                "validator": validator.node_id,
-                "status": "pending"
-            }
+                    results[validator.node_id] = f"RPC error: {result['error']}"
+                else:
+                    logger.info(f"✓ Vote accepted by {validator.node_id}: {result.get('result')}")
+                    results[validator.node_id] = result.get("result")
 
             except Exception as e:
-            logger.error(f"Failed to submit vote to {validator.node_id}: {e}")
-            raise
+                logger.warning(f"Failed to submit to {validator.node_id}: {e}")
+                results[validator.node_id] = str(e)
+
+        # Check if at least one validator accepted the vote
+        successful = [v for v in results.values() if not str(v).startswith(("RPC error", "Failed"))]
+        if successful:
+            logger.info(f"✓ Vote submitted successfully to {len(successful)} validators: {transaction_id}")
+            return {
+                "transaction_id": transaction_id,
+                "block_hash": successful[0] if successful else None,
+                "validator": self.healthy_validators[0].node_id,
+                "status": "pending"
+            }
+        else:
+            logger.error(f"Failed to submit vote to any validator")
+            raise Exception(f"All validator submissions failed: {results}")
 
     async def get_transaction_receipt(
         self,