The kit of a flow: a trigger that starts it, steps, and conditions with two ways out, joined by edges in the order they run.
Its nodes are of types "flow-trigger", "flow-step" and
"flow-condition", with the data:
%{"title" => "Invoice paid", "detail" => "Stripe webhook"}A trigger has a way out and no way in; a step one of each; a condition
a way in and two ways out, with the handles "yes" and "no". People
write the title and the detail in place.
In Markdown, a flow is a Mermaid flowchart: a trigger is a stadium
((["..."])), a condition a rhombus ({"..."}), a step a box, and the
ways out of a condition are labelled Yes and No. from_markdown/1
reads it back, and reads flowcharts people write.