Fix stream compatibility and vision model exposure

internal/util/text.go

@@ -0,0 +1,46 @@
+package util
+
+import "unicode/utf8"
+
+// TruncateRunes trims a string to at most limit Unicode code points.
+func TruncateRunes(text string, limit int) (string, bool) {
+	if limit < 0 {
+		return text, false
+	}
+	if limit == 0 {
+		return "", text != ""
+	}
+
+	count := 0
+	for i := range text {
+		if count == limit {
+			return text[:i], true
+		}
+		count++
+	}
+	return text, false
+}
+
+// TruncateUTF8Bytes trims a string to fit within limit bytes without cutting
+// through a UTF-8 code point boundary.
+func TruncateUTF8Bytes(text string, limit int) (string, bool) {
+	if limit < 0 {
+		return text, false
+	}
+	if len(text) <= limit {
+		return text, false
+	}
+	if limit == 0 {
+		return "", true
+	}
+
+	raw := []byte(text)
+	cut := limit
+	if cut > len(raw) {
+		cut = len(raw)
+	}
+	for cut > 0 && cut < len(raw) && !utf8.RuneStart(raw[cut]) {
+		cut--
+	}
+	return string(raw[:cut]), true
+}