“direction [that] must at the same time give us the guarantee that we are moving within philosophy and not outside of it and around it”.
That's unless I'm a victim of “binary thinking” here. Perhaps Heidegger's metaphilosophy is both above/beyond philosophy and “within philosophy” at one and the same time. This toing and froing beyond and within philosophy may be the only way to reach deep Heideggerian conclusions about philosophy. Jacques Derrida also said (in his 'Structure, Sign, and Play in the Discourse of the Human Sciences' - 1970) that one can never transcend Western metaphysics because the borrowing of even a single concept from it brings along with it the entire package. That is, “the entire syntax and system of Western metaphysics” is brought in when we philosophise about Western philosophy.