Neat, but you can just do this in mermaid too. Taking one of your examples:

  <mermaid>
  flowchart LR

  web([Frontend])

  subgraph platform [Cloud Platform]
    api([API Server])
    db[(Database)]
    api --> db
  end

  web -->|HTTPS| api
  </mermaid>

Fair point. I added basic mermaid parsing to the library so you can do that here too.

    $ echo 'flowchart LR
        web([Frontend])
        subgraph platform [Cloud Platform]
          api([API Server])
          db[(Database)]
          api --> db
        end
        web -->|HTTPS| api' | npx box-of-rain --mermaid

                           ╔══ Cloud Platform ════════════════════╗
                           ║                                      ║
    ╭──────────╮           ║  ╭────────────╮      ╔════════════╗  ║
    │          │           ║  │            │      ║            ║  ║
    │ Frontend │ ─── HTTPS ──▶│ API Server │ ────▶║  Database  ║  ║
    │          │           ║  │            │      ║            ║  ║
    ╰──────────╯           ║  ╰────────────╯      ╚════════════╝  ║
                           ╚══════════════════════════════════════╝