: Halsey has the geas/imprint of the Librarian, John has that of the IsoDidact;
: it was inevitable that those two would find each other again. Also
: explains the deeper connection John has with Cortana.

: Just a thought. ;)

Just thinking aloud here, but weren't all of the Humans with geas imprints gathered up in the beginning of the book? Which means that most of them were Composed, and only a minority of the Lesser Ark survivors had the imprints.

Unless tinkering was done post-Firing.