My biggest gripe with this is definitely the timeline. Largely because, while I understand that it effectively works as a way to build tension for the ending, the events in the timeline itself feel very straight forward. Given the fact that we know how the timeline ends, I didn’t feel like the foundation’s response was specifically tailored to the anomaly (which sort of makes sense because the mechanics of the anomaly means that nothing can really be done). But because of this, the timeline events were either descriptions of the head expanding (which isn’t particularly new information given that we know this is what was going to happen from the beginning), or somewhat generic foundation responses (calling in an mtf, suppressing information, debating nuclear strikes, etc).
I feel like I would have enjoyed this more if you didn’t lead with the fact that the brain gets this large and explodes. Largely because the moment you say that, I have an idea in my head of what the timeline is going to look like. Once I have this idea in my head, the only thing that surprised me was the ending. But if you never mentioned the fact that the brain gets big enough to cause a BM scenario, or explode at all, and just assert that it expands, then that would have allowed you to explore the dramatic escalation without telegraphing a lot of it to the reader.