GR translation: firm among the stoneswept hair

[Mike Jing]

P221.13-20  Nora still carries on her Adventure, her “Ideology of the
Zero,” firm among the stoneswept hair of the last white guardians at
the last stepoff into the black, into the radiant. . . . But where
will Leni be now? Where will she have wandered off to, carrying her
child, and her dreams that will not grow up? Either we didn’t mean to
lose her—either it was an ellipsis in our care, in what some of us
will even swear is our love, or someone has taken her, deliberately,
for reasons being kept secret, and Sachsa’s death is part of it too.

What is the meaning of "stoneswept" in "stoneswept hair"?