How come Firestore won't write anything anymore?

I had been scratching my head since last night. For some reason, when creating lots of new documents, only the first batch would show up in my UI. I'd put a print before and after the await batch.commit() and see that it would hang. What was going on?

It turns out I had run out of free quota. It'd have been nice to throw an exception or print out a warning instead of locally committing, and never returning.