fix(agent): prevent duplicate tool schema injection in XML dispatcher (#3744)

Remove duplicate tool listing from XmlToolDispatcher::prompt_instructions()
since tool listing is already handled by ToolsSection in prompt.rs. The
method now only emits the XML protocol envelope.

Also fix UTF-8 char boundary panics in memory consolidation truncation by
using char_indices() instead of manual byte-boundary scanning.

Fixes #3643
Supersedes #3678

Co-authored-by: TJUEZ <TJUEZ@users.noreply.github.com>

src/agent/dispatcher.rs

@@ -128,7 +128,7 @@ impl ToolDispatcher for XmlToolDispatcher {
         ConversationMessage::Chat(ChatMessage::user(format!("[Tool results]\n{content}")))
     }
 
-    fn prompt_instructions(&self, tools: &[Box<dyn Tool>]) -> String {
+    fn prompt_instructions(&self, _tools: &[Box<dyn Tool>]) -> String {
         let mut instructions = String::new();
         instructions.push_str("## Tool Use Protocol\n\n");
         instructions
@@ -136,17 +136,6 @@ impl ToolDispatcher for XmlToolDispatcher {
         instructions.push_str(
             "```\n<tool_call>\n{\"name\": \"tool_name\", \"arguments\": {\"param\": \"value\"}}\n</tool_call>\n```\n\n",
         );
-        instructions.push_str("### Available Tools\n\n");
-
-        for tool in tools {
-            let _ = writeln!(
-                instructions,
-                "- **{}**: {}\n  Parameters: `{}`",
-                tool.name(),
-                tool.description(),
-                tool.parameters_schema()
-            );
-        }
 
         instructions
     }

src/agent/tests.rs

@@ -1282,8 +1282,12 @@ fn xml_dispatcher_generates_tool_instructions() {
 
     assert!(instructions.contains("## Tool Use Protocol"));
     assert!(instructions.contains("<tool_call>"));
-    assert!(instructions.contains("echo"));
-    assert!(instructions.contains("Echoes the input"));
+    // Tool listing is handled by ToolsSection in prompt.rs, not by the
+    // dispatcher.  prompt_instructions() must only emit the protocol envelope.
+    assert!(
+        !instructions.contains("echo"),
+        "dispatcher should not duplicate tool listing"
+    );
 }
 
 #[test]

src/memory/consolidation.rs

@@ -45,10 +45,12 @@ pub async fn consolidate_turn(
     // Truncate very long turns to avoid wasting tokens on consolidation.
     // Use char-boundary-safe slicing to prevent panic on multi-byte UTF-8 (e.g. CJK text).
     let truncated = if turn_text.len() > 4000 {
-        let mut end = 4000;
-        while end > 0 && !turn_text.is_char_boundary(end) {
-            end -= 1;
-        }
+        let end = turn_text
+            .char_indices()
+            .map(|(i, _)| i)
+            .take_while(|&i| i <= 4000)
+            .last()
+            .unwrap_or(0);
         format!("{}…", &turn_text[..end])
     } else {
         turn_text.clone()
@@ -99,10 +101,12 @@ fn parse_consolidation_response(raw: &str, fallback_text: &str) -> Consolidation
         // Fallback: use truncated turn text as history entry.
         // Use char-boundary-safe slicing to prevent panic on multi-byte UTF-8.
         let summary = if fallback_text.len() > 200 {
-            let mut end = 200;
-            while end > 0 && !fallback_text.is_char_boundary(end) {
-                end -= 1;
-            }
+            let end = fallback_text
+                .char_indices()
+                .map(|(i, _)| i)
+                .take_while(|&i| i <= 200)
+                .last()
+                .unwrap_or(0);
             format!("{}…", &fallback_text[..end])
         } else {
             fallback_text.to_string()