feat: add next batch link verification

- Add next_batch_link field to CombinedInput struct
- Fetch parent hash of next block in batch processor
- Add verification check for next batch link in MMR append method
- Ensure proper chain continuity between batches

config/anvil.messaging.docker.json

@@ -5,5 +5,5 @@
   "sender_address": "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
   "private_key": "0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80",
   "interval": 2,
-  "from_block": 7477808
+  "from_block": 7480941
 }

crates/client/src/client.rs

@@ -129,7 +129,7 @@ impl LightClient {
         let to_block = if self.blocks_per_run > 0 {
             BlockId::Number(std::cmp::min(
                 self.latest_processed_block + self.blocks_per_run,
-                latest_block
+                latest_block,
             ))
         } else {
             BlockId::Number(latest_block)
@@ -163,8 +163,9 @@ impl LightClient {
                 .unwrap_or(self.latest_processed_block);
 
             // Check if we've reached the block limit for this run
-            if self.blocks_per_run > 0 && 
-               new_latest_block > self.latest_processed_block + self.blocks_per_run {
+            if self.blocks_per_run > 0
+                && new_latest_block > self.latest_processed_block + self.blocks_per_run
+            {
                 info!(
                     "Reached block limit for this run. Stopping at block {}",
                     self.latest_processed_block + self.blocks_per_run

crates/client/src/main.rs

@@ -41,11 +41,12 @@ async fn main() -> Result<()> {
     tracing::info!("Starting Fossil Light Client...");
 
     let mut client = LightClient::new(
-        args.polling_interval, 
+        args.polling_interval,
         args.batch_size,
         args.start_block,
         args.blocks_per_run,
-    ).await?;
+    )
+    .await?;
     client.run().await?;
     Ok(())
 }

crates/guest-types/src/lib.rs

@@ -114,6 +114,7 @@ pub struct CombinedInput {
     headers: Vec<BlockHeader>,
     mmr_input: MMRInput,
     batch_link: Option<String>,
+    next_batch_link: Option<String>,
     skip_proof_verification: bool,
 }
 
@@ -124,6 +125,7 @@ impl CombinedInput {
         headers: Vec<BlockHeader>,
         mmr_input: MMRInput,
         batch_link: Option<String>,
+        next_batch_link: Option<String>,
         skip_proof_verification: bool,
     ) -> Self {
         Self {
@@ -132,6 +134,7 @@ impl CombinedInput {
             headers,
             mmr_input,
             batch_link,
+            next_batch_link,
             skip_proof_verification,
         }
     }
@@ -156,6 +159,10 @@ impl CombinedInput {
         self.batch_link.as_deref()
     }
 
+    pub fn next_batch_link(&self) -> Option<&str> {
+        self.next_batch_link.as_deref()
+    }
+
     pub fn skip_proof_verification(&self) -> bool {
         self.skip_proof_verification
     }

crates/methods/mmr-append/src/main.rs

@@ -58,6 +58,16 @@ fn main() {
         }
     }
 
+    // Add next batch link check
+    match (input.next_batch_link(), &last_header.block_hash) {
+        (Some(next_link), _) => {
+            assert!(next_link == last_header.block_hash, "Next batch link mismatch");
+        }
+        (None, _) => {
+            // It's okay if there's no next batch link - might be the latest block
+        }
+    }
+
     // Create output
     let output = GuestOutput::new(
         first_batch_index,

crates/publisher/src/core/batch_processor.rs

@@ -172,12 +172,19 @@ impl<'a> BatchProcessor<'a> {
             None
         };
 
+        let next_batch_link = db_connection
+            .get_block_header_by_number(adjusted_end_block + 1)
+            .await?
+            .map(|header| header.parent_hash)
+            .flatten();
+
         let combined_input = CombinedInput::new(
             chain_id,
             self.batch_size,
             headers.clone(),
             mmr_input,
             batch_link,
+            next_batch_link,
             self.skip_proof_verification,
         );