I admit I don't know a lot about the math behind Curve25519 and the DH exchange based on it.
I'm asking if after publishing the result of this operation:
ephemeral_share = X25519(ephemeral_secret, BASEPOINT)
ephemeral_secret be found by whomever obtains
ephemeral_share, given that they know the used curve (and therefore the curve's base point)?
It's not that I don't trust Filippo's judgment (the above is taken from a 2019 entry on his blog); I'm just trying to make sure I understand things correctly.