From ef0fcb8ee9f01d07b09f9b606bcc71f91f674e50 Mon Sep 17 00:00:00 2001
From: Blake <0xblake.sg@gmail.com>
Date: Fri, 10 Jul 2026 13:03:34 +0800
Subject: [PATCH] Fix: handle empty watchtower challenge txids

---
 circuits/operator-proof/host/src/lib.rs |  6 ++++-
 proof-builder-rpc/src/task/mod.rs       | 32 +++++++++++++------------
 2 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/circuits/operator-proof/host/src/lib.rs b/circuits/operator-proof/host/src/lib.rs
index 9c006875..73231f63 100644
--- a/circuits/operator-proof/host/src/lib.rs
+++ b/circuits/operator-proof/host/src/lib.rs
@@ -94,11 +94,15 @@ fn parse_indexed_watchtower_inputs(
     watchtower_challenge_txids: &str,
     watchtower_public_keys: &str,
 ) -> anyhow::Result<(Vec<(u16, Txid, PublicKey)>, Vec<[u8; 32]>)> {
-    let txids = watchtower_challenge_txids.split(',').collect::<Vec<_>>();
     let public_keys = watchtower_public_keys
         .split(',')
         .map(PublicKey::from_str)
         .collect::<Result<Vec<_>, _>>()?;
+    let txids = if watchtower_challenge_txids.trim().is_empty() {
+        vec![""; public_keys.len()]
+    } else {
+        watchtower_challenge_txids.split(',').collect::<Vec<_>>()
+    };
     anyhow::ensure!(
         txids.len() == public_keys.len(),
         "watchtower challenge txids and public keys must have equal lengths"
diff --git a/proof-builder-rpc/src/task/mod.rs b/proof-builder-rpc/src/task/mod.rs
index 949c9d49..a6f795f3 100644
--- a/proof-builder-rpc/src/task/mod.rs
+++ b/proof-builder-rpc/src/task/mod.rs
@@ -378,16 +378,13 @@ pub(crate) async fn fetch_on_demand_task(
         }
     }
 
-    // double check the committed block height is larger than all the watchtower challenge txns'.
-    match operator_committed_blockhash {
-        Some(ref hash) => match btc_client.get_block_by_hash(&BlockHash::from_str(hash)?).await {
-            Ok(Some(block)) => {
-                if block.bip34_block_height()? != largest_btc_block_height as u64 {
-                    anyhow::bail!(
-                        "Operator committed block {hash} is not confirmed yet, wait for the next round"
-                    );
-                }
-            }
+    let btc_proof_height = if is_watchtower {
+        largest_btc_block_height
+    } else {
+        let hash = operator_committed_blockhash.as_ref().unwrap();
+        let committed_height = match btc_client.get_block_by_hash(&BlockHash::from_str(hash)?).await
+        {
+            Ok(Some(block)) => block.bip34_block_height()? as u32,
             Ok(None) => {
                 tracing::warn!(
                     "Operator committed block hash {hash} is not found in BTC, it might be mempool tx, wait for the next round"
@@ -400,13 +397,18 @@ pub(crate) async fn fetch_on_demand_task(
                 );
                 return Ok(None);
             }
-        },
-        None => {} // skip for watchtowers
+        };
+        if committed_height < largest_btc_block_height {
+            anyhow::bail!(
+                "operator committed block height {committed_height} is lower than challenge tx height {largest_btc_block_height}"
+            );
+        }
+        committed_height
     };
 
     let header_chain_input_proof = match storage_processor
         .find_long_running_task_proof_including_block_number(
-            largest_btc_block_height as i64,
+            btc_proof_height as i64,
             HeaderChainProofBuilder::name(),
         )
         .await?
@@ -415,7 +417,7 @@ pub(crate) async fn fetch_on_demand_task(
         None => {
             tracing::warn!(
                 "Header chain proof is not ready for block: {}, proof not ready",
-                largest_btc_block_height
+                btc_proof_height
             );
             return Ok(None);
         }
@@ -466,7 +468,7 @@ pub(crate) async fn fetch_on_demand_task(
     // commit chain
     let commit_chain_input_proof = match storage_processor
         .find_long_running_task_proof_including_block_number(
-            largest_btc_block_height as i64,
+            btc_proof_height as i64,
             CommitChainProofBuilder::name(),
         )
         .await?