Improve VRF test comments and add comprehensive chaining test

- Fixed comment on line 554 to clarify VRF chaining vs randomness
- Kept test_vrf_deterministic for basic determinism testing
- Added new test_vrf_chaining to comprehensively test VRF chaining:
  - Produces 3 blocks in sequence
  - Verifies each block has unique VRF output due to chaining
  - Recreates chain to verify deterministic behavior with chaining
  - Tests both uniqueness (chaining works) and determinism (same chain = same VRFs)

Co-authored-by: Steake <530040+Steake@users.noreply.github.com>

Author: Copilot

crates/bitcell-node/src/blockchain.rs

@@ -551,7 +551,7 @@ mod tests {
             sk.public_key(),
         ).unwrap();
 
-        // VRF outputs should be different (demonstrates randomness)
+        // VRF outputs should be different because block2 uses block1's VRF output as input (VRF chaining)
         assert_ne!(block2.header.vrf_output, blockchain.get_block(1).unwrap().header.vrf_output);
 
         // Validate second block
@@ -574,4 +574,50 @@ mod tests {
         // Same key, same previous state should produce same VRF output
         assert_eq!(block1.header.vrf_output, block2.header.vrf_output);
     }
+    
+    #[test]
+    fn test_vrf_chaining() {
+        // Test that VRF properly chains - each block's VRF uses previous block's VRF output as input
+        let sk = Arc::new(SecretKey::generate());
+        let metrics = MetricsRegistry::new();
+        let blockchain = Blockchain::new(sk.clone(), metrics);
+        
+        // Produce first block
+        let block1 = blockchain.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_ne!(block1.header.vrf_output, [0u8; 32], "Block 1 VRF should be non-zero");
+        blockchain.add_block(block1.clone()).unwrap();
+        
+        // Produce second block
+        let block2 = blockchain.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_ne!(block2.header.vrf_output, [0u8; 32], "Block 2 VRF should be non-zero");
+        assert_ne!(block2.header.vrf_output, block1.header.vrf_output, 
+                   "Block 2 VRF should differ from Block 1 due to chaining");
+        blockchain.add_block(block2.clone()).unwrap();
+        
+        // Produce third block
+        let block3 = blockchain.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_ne!(block3.header.vrf_output, [0u8; 32], "Block 3 VRF should be non-zero");
+        assert_ne!(block3.header.vrf_output, block1.header.vrf_output, 
+                   "Block 3 VRF should differ from Block 1");
+        assert_ne!(block3.header.vrf_output, block2.header.vrf_output, 
+                   "Block 3 VRF should differ from Block 2 due to chaining");
+        
+        // Verify that recreating the chain produces the same VRF sequence (determinism with chaining)
+        let metrics2 = MetricsRegistry::new();
+        let blockchain2 = Blockchain::new(sk.clone(), metrics2);
+        
+        let block1_v2 = blockchain2.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_eq!(block1_v2.header.vrf_output, block1.header.vrf_output,
+                   "First block VRF should be deterministic");
+        blockchain2.add_block(block1_v2).unwrap();
+        
+        let block2_v2 = blockchain2.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_eq!(block2_v2.header.vrf_output, block2.header.vrf_output,
+                   "Second block VRF should be deterministic given same chain state");
+        blockchain2.add_block(block2_v2).unwrap();
+        
+        let block3_v2 = blockchain2.produce_block(vec![], vec![], sk.public_key()).unwrap();
+        assert_eq!(block3_v2.header.vrf_output, block3.header.vrf_output,
+                   "Third block VRF should be deterministic given same chain state");
+    }
 }