This is beautiful, genuinely (the SVGs are lovely bits of artwork) and it's a fun puzzle to read, and I've shared with friends that like esolangs, including your book (good luck on publishing!).

In the "Data Strands" -> "Value Strands" section, you describe it as "Value strands (and other data strands), begin with a hook that points up (as in the third strand below) or to the left (as in the first two)" for the following example:

  1 ╵╰──╮╭──╯╶╮
  2    ─┘└─   └─╮
  3               
  5              ╷

but the way I was parsing it was that the hook is '╰' or '╯', in which case both of those are hooks pointing up? It looks like a fairly innocuous typo, but I'm never sure with an esolang so wanted to ask.