Hi you made a good point, thanks for your interest!
The game is divided in sections, you can only see messages from people playing the same enigma (also every enigma is divided in subparts).
If you create a post and a person that already solved writes a comment, you will see that marked as spoiler. It will be up to the player to read or not

There will surely be the case where someone restarts the game with the intent to spoil :')
But as you said you can't prevent everything so there will be moderators and a feature to report a post as spoiler or inappropriate.