fix: chain tip race condition

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## v0.14.8 (TBD)
+
+- Fixed a startup race in the network transaction builder that could panic the chain MMR when a block committed between subscribing to the mempool and fetching the chain tip from the store ([#1953](https://github.com/0xMiden/node/pull/1953)).
+
 ## v0.14.7 (2026-04-15)
 
 - [BREAKING] Aligned proto `TransactionHeader` with domain type and exposed erased notes in `SyncTransactions` ([#1941](https://github.com/0xMiden/node/pull/1941)).

Cargo.toml

@@ -32,7 +32,7 @@ license      = "MIT"
 readme       = "README.md"
 repository   = "https://github.com/0xMiden/node"
 rust-version = "1.93"
-version      = "0.14.7"
+version      = "0.14.8"
 
 # Optimize the cryptography for faster tests involving account creation.
 [profile.test.package.miden-crypto]

crates/ntx-builder/src/builder.rs

@@ -297,6 +297,19 @@ impl NetworkTransactionBuilder {
     async fn update_chain_tip(&mut self, tip: BlockHeader) {
         let mut chain_state = self.chain_state.write().await;
 
+        // Skip blocks already reflected in the chain state. A `BlockCommitted` event may arrive
+        // for a block whose state was already loaded from the store during startup: the mempool
+        // subscription is established first and then the chain tip is fetched, so any block
+        // committed in that window produces an event for state we have already ingested.
+        if tip.block_num() <= chain_state.chain_tip_header.block_num() {
+            tracing::debug!(
+                event_block = %tip.block_num(),
+                current_tip = %chain_state.chain_tip_header.block_num(),
+                "skipping BlockCommitted event for block already in chain state",
+            );
+            return;
+        }
+
         // Update MMR which lags by one block.
         let mmr_tip = chain_state.chain_tip_header.clone();
         Arc::make_mut(&mut chain_state.chain_mmr).add_block(&mmr_tip, true);