mcvA sensitive flag sounds like a great idea, but repurposing a summary as content warning based on a flag sounds like a bad idea to me. If there's no explicit content warning field, I think a spoiler tag is a better fit, because that already functions similarly without the flag.
But I'd prefer an explicit content warning field. There's clearly a need for it, and if it's explicit, you could set your client to always show or hide certain content.
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