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Hi David/Galina, FYI, I found one big reason why self-hosting bots fail long after the offending commit is tested: dirty builds. In a dirty build (no make clean), when a file X is changed that breaks file Y, the bot will only accuse the failure when file Y is changed, too, so that stage1 with modified X will compile file Y, and break. At hindsight, it's obvious. But I hadn't connected