error_get_full_trace Function

   function error_get_full_trace(this) result(trace)
      !! Get complete error message with stack trace
      !! Returns a multi-line string with error and call stack
      class(error_t), intent(in) :: this
      character(len=:), allocatable :: trace
      character(len=2048) :: buffer
      integer :: i, pos

      if (.not. this%has_error()) then
         trace = ""
         return
      end if

      ! Build error message
      write (buffer, '(A,I0,A)') "Error ", this%code, ": "
      pos = len_trim(buffer) + 1

      if (allocated(this%message)) then
         buffer(pos:) = this%message
         pos = len_trim(buffer) + 1
      end if

      ! Add stack trace if available
      if (this%stack_depth > 0) then
         buffer(pos:) = new_line('a')//"Call stack (most recent first):"
         pos = len_trim(buffer) + 1

         do i = this%stack_depth, 1, -1
            write (buffer(pos:), '(A,I0,A)') new_line('a')//"  [", i, "] "
            pos = len_trim(buffer) + 1
            buffer(pos:) = trim(this%call_stack(i))
            pos = len_trim(buffer) + 1
         end do
      end if

      trace = trim(buffer)
   end function error_get_full_trace