Is it just me, or has it always seemed weird that the Forerunners keep the only way to stop the Flood in a facility full of it? I understand that it’s a place for research, but it would make a lot more sense to house the Index in a secure place in the event of an outbreak.
I might not be fully informed on all of the functions of the library facility (besides storing the index and data files) on each Halo ring but I’ve always assumed that in Halo 1 the flood simply had spread into that part of the ring.
In Halo 2 it was just 2401 Penitent Tangent ignoring an outbreak and then having to wall the flood off so that they didn’t spread. So its likely that a flood facility was near the index / library facility on Installation 05 and they broke out and simply spread throughout that whole tundra area before being walled in, and they had a gravemind so it would understand the importance of getting the index so that the ring can’t be fired.
Keep in mind, the Flood would have likely congregated anywhere the Index was stored (they are biological avatars of the Precursors). As for the Forerunners’ layout, the Flood samples they had stored were supposed to be harmless, completely contained, so the Index being past them shouldn’t have been any more dangerous than having a gun-locker past rows of predators locked in cages that only you have the keys to (Shouldn’t be dangerous, but I’ll agree that a different layout would have likely been wiser)
I dont think the Library had much ACTIVE Flood, we only ever see them after the Flood has gotten in. And on the two Instillations we see protocol has kind of broken down. I don’t THINK the Reclaimer is supposed to fight his way through hordes of Flood to get the Index…