The headless viewer suite covered only the DOT half (normalizeModel/
genDot); the tooltip half — INFO.B (collapsed), INFO.C (expanded
cluster), INFO.P (ports), and md()'s markdown-to-HTML step — was
asserted by no test. viewer_tooltip.mjs pins the current shapes;
graph-viewer.js only hoists md() above the browser guard and exports
it (location-only move, no behaviour change), so the pin can drive the
real conversion headlessly. Surfaced by the grounding-check on the #125
composite-doc spec: its viewer assumptions had no current-behaviour pin.
refs #125
