[woopsn]

I tried a few techniques, in terms of accessibility I think "old" ways are the best here.

    <div class=flowchart>... crazy modern shit ...</div>

    <ol class=sr-only>
      <li id=step1> Water on stove.
        <ol>
          <li>Boiling? Proceed to <a href=#step2>Step 2</a></li>
          <li>Otherwise return to <a href=#step1>Step 1</a></li>
        </ol>
      </li>

      <li id=step2> Cook dumplings in water. Wait a minute.
        Floating? Proceed to <a href=#step4>Step 4</a>.</li>
        Otherwise proceed to <a href=#step3>Step 3</a>.</li>
      </li>

      <li id=step3> Stir dumplings. Return to <a href=#step2>Step 2</a>.</li>

      ...
   </ol>

(or start with the anchors/list, and progressively enhance)