修复: byte/rune 长度混淆及错误位置丢失

internal/poserror.go

@@ -0,0 +1,19 @@
+package internal
+
+import "fmt"
+
+// PosError is an internal error type that carries source position information.
+// Lexer and parser return this so that the public wrapParseError can extract the position.
+type PosError struct {
+	Line    int
+	Col     int
+	Message string
+}
+
+func (e *PosError) Error() string {
+	return fmt.Sprintf("line %d, col %d: %s", e.Line, e.Col, e.Message)
+}
+
+func PosErrorf(line, col int, format string, args ...any) *PosError {
+	return &PosError{Line: line, Col: col, Message: fmt.Sprintf(format, args...)}
+}