Fix message ack bound check

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   duplicates to peers.
 - Make sure the configuration for Quic connections is the same for outbound and
   inbound connections.
+- Fix bound check on message ACK.
 
 ## [0.7.4] - 2026-03-23
 

mycelium/src/message.rs

@@ -359,7 +359,7 @@ where
                 let mc = MessageChunk::new(mp);
                 // Sanity checks. This is just to protect ourselves, if the other party is
                 // malicious it can return any data it wants here.
-                if mc.chunk_idx() > message.chunks.len() as u64 {
+                if mc.chunk_idx() >= message.chunks.len() as u64 {
                     debug!("Dropping CHUNK ACK for message because ACK'ed chunk is out of bounds");
                     return;
                 }