I played a skirmish against AI an I researched the tech to garrison scholars in military buildings. I garrisoned a scholar in the siege workshop. When I went to research geometry I couldn’t find the tech.
When I watched the reply it was in the siege workshop. Turns out when you garrison a scholar, the geometry button gets replaced by the ungarrison scholar button.
Since I never ungarrisoned the scholar in the game, I can’t say what happens after that. I’m assuming geometry comes back when you ungarrison the scholar, but that needs testing.