Mages automatically learn new spells as they gain levels; they can also "be taught by a mage who already knows the spell ... or they must find a grimoire laying out the fine details of the incantation."

It seems implied that a fledgling mage would be able to steal or otherwise take another mage's spellbook and copy their grimoire, but it is never explicitly stated. (Or if it is, I haven't found it!) Is this the intended design?

Obviously, I can always make the ruling myself. It's cool to think that spells can only be passed willingly by mages; or else learned from very specifically written grimoires designed to teach the reader. So if a wizard dies and their spellbook is stolen, it's simply a smattering of gibberish and eclectic notes to any other reader. And thus all that arcane knowledge is lost!