Okay, at least the markdown formatting was just due to posting it from the command line in a primitive way.
Reminder: to publish a pre-written json object as an ssb message, use this:

ssb-server publish . < /tmp/block.json

where /tmp/block.json holds the message content like such:

{
  "type": "contact",
  "contact": "@kekD9RP76YUft10KeT1t8WJOGDqsHQndcJcmbQi6hyk=.ed25519",
  "blocking": true,
  "reason": "# Test Block\n\nThis is *yet another* _random_ ID that I'm blocking **for test purposes**."
}