From 11e40050e3fd83a7a2df709b62708b8e1dfb8646 Mon Sep 17 00:00:00 2001
From: PratikDhanave <i.pratikdhanave@gmail.com>
Date: Tue, 22 Sep 2026 08:48:10 +0530
Subject: [PATCH] Truncate example output on rune boundaries in verifyexamples

truncate sliced by byte index, which can split a multi-byte UTF-8 rune
(examples print degree signs, emoji, etc.) and emit invalid UTF-8 into logs,
CSV, and the AI-verifier prompt. Back off to a rune boundary before cutting.
---
 cmd/verifyexamples/verifier.go      |  9 ++++++++-
 cmd/verifyexamples/verifier_test.go | 17 +++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/cmd/verifyexamples/verifier.go b/cmd/verifyexamples/verifier.go
index 4e207c26..88ad7ec6 100644
--- a/cmd/verifyexamples/verifier.go
+++ b/cmd/verifyexamples/verifier.go
@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/microsoft/agent-framework-go/agent"
 )
@@ -139,5 +140,11 @@ func truncate(text string, maxLength int) string {
 	if len(text) <= maxLength {
 		return text
 	}
-	return text[:maxLength] + "... (truncated)"
+	// Back off to a rune boundary so truncation never splits a multi-byte rune
+	// (examples print °C, emoji, etc.) and emits invalid UTF-8 into logs/CSV.
+	end := maxLength
+	for end > 0 && !utf8.RuneStart(text[end]) {
+		end--
+	}
+	return text[:end] + "... (truncated)"
 }
diff --git a/cmd/verifyexamples/verifier_test.go b/cmd/verifyexamples/verifier_test.go
index e1b84fa6..ae8e84c7 100644
--- a/cmd/verifyexamples/verifier_test.go
+++ b/cmd/verifyexamples/verifier_test.go
@@ -4,7 +4,9 @@ package main
 
 import (
 	"context"
+	"strings"
 	"testing"
+	"unicode/utf8"
 )
 
 func TestVerifyDeterministicOutput(t *testing.T) {
@@ -33,3 +35,18 @@ func TestVerifyRequiresAIAgentForSemanticChecks(t *testing.T) {
 		t.Fatalf("Failures = %#v, want one", result.Failures)
 	}
 }
+
+func TestTruncateDoesNotSplitRunes(t *testing.T) {
+	// "°" is two bytes (0xC2 0xB0); truncating at byte 1 must not split it.
+	got := truncate("a°cdef", 2)
+	if !utf8.ValidString(got) {
+		t.Fatalf("truncate produced invalid UTF-8: %q", got)
+	}
+	if !strings.HasPrefix(got, "a") || strings.ContainsRune(got, '�') {
+		t.Fatalf("truncate = %q, want a clean rune-boundary cut", got)
+	}
+	// Short input is returned unchanged.
+	if truncate("ok", 10) != "ok" {
+		t.Fatalf("short input was modified")
+	}
+}