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Conclusion: Google let go of their bill as a one-time gesture.

tldr: Infinite, exponential recursion without a break in their code. They used Google Cloud Run (with a budget of $100 per month) and Firebase (free plan). Google automatically upgraded the Firebase free plan to pay-as-you-go because Cloud Run decided to do so (haha). Google Billing, which cuts off the project if the budget/limit is reached, had a one-day delay (Firebase Dashboard as well)!