So basically, if you're WFH, every single word you utter over a chat is now "corporate document" which effectively means you're now codifying complete surveillance of everything you say for a third of your life?

Google has previously shown in released messages that it knows chats are a "safer" place to discuss sensitive topics and employees were given the ability to not preserve them, and so Google knowingly misled the DOJ and intentionally still deleted the chats probably thinking they could just get away with it. That's clearly what the DOJ is also arguing.

When your company is being sued, yes, corporate communication channels become increasingly monitored and not just a line in the employment agreement.

Do you happen to have a reference?