fix: handle negative truncate lengths (#744)

internal/util/strings.go

@@ -5,6 +5,9 @@ package util
 
 // TruncateStr truncates s to at most n runes, safe for multi-byte (e.g. CJK) characters.
 func TruncateStr(s string, n int) string {
+	if n <= 0 {
+		return ""
+	}
 	r := []rune(s)
 	if len(r) <= n {
 		return s
@@ -14,6 +17,9 @@ func TruncateStr(s string, n int) string {
 
 // TruncateStrWithEllipsis truncates s to at most n runes (including "..." suffix).
 func TruncateStrWithEllipsis(s string, n int) string {
+	if n <= 0 {
+		return ""
+	}
 	r := []rune(s)
 	if len(r) <= n {
 		return s

internal/util/strings_test.go

@@ -17,6 +17,7 @@ func TestTruncateStr(t *testing.T) {
 		{"truncate", "hello world", 5, "hello"},
 		{"empty", "", 5, ""},
 		{"zero limit", "hello", 0, ""},
+		{"negative limit", "hello", -1, ""},
 		{"CJK characters", "你好世界测试", 4, "你好世界"},
 	}
 	for _, tt := range tests {
@@ -41,6 +42,8 @@ func TestTruncateStrWithEllipsis(t *testing.T) {
 		{"limit less than 3", "hello", 2, "he"},
 		{"limit equals 3", "hello world", 3, "..."},
 		{"empty", "", 5, ""},
+		{"zero limit", "hello", 0, ""},
+		{"negative limit", "hello", -1, ""},
 		{"CJK with ellipsis", "你好世界测试", 5, "你好..."},
 	}
 	for _, tt := range tests {