[dexen]

"Append-only files" would be a great fit here: to ensure regular users and bots don't modify others' posts. Sadly this Plan 9 functionality is not ported to Linux yet. That's a permission bit, similar to "read" or "write", but even more specific.

[HerrMonnezza]

IIRC, Linux' ext2/3/4 support an 'a' attribute that make a file append-only.

[ComodoHacker]

Not so great if you're talking about real use cases where moderation is mandatory.

[Pannoniae]

Moderation is never mandatory, it's just something most people desire.

[linschn]

The host owner (there's no root on Plan 9) can change those permissions and edit the file if need be.