fix: Fix panic due to UTF-8 character boundary errors

crates/openfang-runtime/src/context_budget.rs

@@ -5,6 +5,7 @@
 //! - Layer 2: Context guard that scans all tool results before LLM calls
 //!   and compacts oldest results when total exceeds 75% headroom.
 
+use crate::str_utils::safe_truncate_str;
 use openfang_types::message::{ContentBlock, Message, MessageContent};
 use openfang_types::tool::ToolDefinition;
 use tracing::debug;
@@ -217,11 +218,14 @@ fn truncate_to(content: &str, max_chars: usize) -> String {
         .rfind('\n')
         .map(|pos| search_start + pos)
         .unwrap_or(keep);
+
+    // Use safe_truncate_str as an extra layer of safety
+    let safe_content = safe_truncate_str(content, break_point);
     format!(
         "{}\n\n[COMPACTED: {} → {} chars by context guard]",
-        &content[..break_point],
+        safe_content,
         content.len(),
-        break_point
+        safe_content.len()
     )
 }
 

crates/openfang-runtime/src/llm_errors.rs

@@ -11,6 +11,8 @@
 
 use serde::Serialize;
 
+use crate::str_utils::safe_truncate_str;
+
 // ---------------------------------------------------------------------------
 // Types
 // ---------------------------------------------------------------------------
@@ -534,7 +536,7 @@ fn cap_message(msg: &str, max: usize) -> String {
             .nth(max - 3)
             .map(|(i, _)| i)
             .unwrap_or(msg.len());
-        format!("{}...", &msg[..end])
+        safe_truncate_str(msg, end).to_string() + "..."
     }
 }
 

crates/openfang-runtime/src/prompt_builder.rs

@@ -4,6 +4,8 @@
 //! Replaces the scattered `push_str` prompt injection throughout the codebase
 //! with a single, testable, ordered prompt builder.
 
+use crate::str_utils::safe_truncate_str;
+
 /// All the context needed to build a system prompt for an agent.
 #[derive(Debug, Clone, Default)]
 pub struct PromptContext {
@@ -627,7 +629,7 @@ fn cap_str(s: &str, max_chars: usize) -> String {
             .nth(max_chars)
             .map(|(i, _)| i)
             .unwrap_or(s.len());
-        format!("{}...", &s[..end])
+        safe_truncate_str(s, end).to_string() + "..."
     }
 }