Behavior notes for builder

• Anchor-to-node: graph.graphToScreenCoords(node) → {x,y}. Popup positioned at (x+16, y+16) clamped to viewport.width − popup.width − 8 and viewport.height − popup.height − 8.
• Click-away close: two approaches — (a) semi-transparent backdrop #popup-backdrop with pointer-events:all behind the popup, onclick closes; (b) document.addEventListener('mousedown', outsideClickHandler) that checks !popup.contains(e.target). Approach (b) has no dim effect. Toggle above demos approach (a).
• Close button (×): always present; top-right of header.
• ESC key: document.addEventListener('keydown', e => { if (e.key==='Escape') closePopup(); }).
• Clicked node halo: pulsing ring .faux-node--active::after stays on the node while popup is open; removed on close.
• Wiki content: async fetch after popup renders — placeholder "Loading…" swapped on resolve (see graph-detail.js _fetchWikiContent).
• Wide wiki mode: add class node-popup--wide (500px) for wiki nodes, or auto-detect on click. Toggle above demos the switch.
• OLD sidebar: document.getElementById('right').classList.remove('open') before opening the popup — suppress the phosphor-green panel entirely in galaxy mode (body.galaxy-active already hides .floating-overlay; #right needs separate handling).