fix: use truncate_safe for safer string truncation in chat/checkpoint.rs. (#3137)

Author: h16rkim

crates/chat-cli/src/cli/chat/checkpoint.rs

@@ -28,6 +28,7 @@ use serde::{
 use tracing::debug;
 
 use crate::cli::ConversationState;
+use super::util::truncate_safe;
 use crate::cli::chat::conversation::HistoryEntry;
 use crate::os::Os;
 
@@ -370,7 +371,7 @@ pub fn truncate_message(s: &str, max_len: usize) -> String {
         return s.to_string();
     }
 
-    let truncated = &s[..max_len];
+    let truncated = truncate_safe(s, max_len);
     if let Some(pos) = truncated.rfind(' ') {
         format!("{}...", &truncated[..pos])
     } else {