Pass ?ref= through to Summit 2026 Pretix widget as campaign code

[rrrutledge]

Summary

Members sharing a Summit 2026 referral link (e.g. https://innersourcecommons.org/events/isc-2026/?ref=ISC26-ADADAI) now have that code carried into the embedded Pretix ticket widget, so Pretix can credit the resulting order to the member's campaign.

• layouts/partials/head.html defines window.pretixWidgetCallback (gated behind .Params.pretixWidget, so only the Summit 2026 page is affected) before the Pretix widget script loads.
• The callback reads ?ref= from the page URL and, only when it matches ^ISC26-[A-Z0-9-]{1,40}$, sets data-campaign on the <pretix-widget> element.
• The callback always calls window.PretixWidget.buildWidgets(), with or without a valid ref, so the widget builds exactly as it does today when no ref is present.
• The page's no-JS fallback link (inside <noscript>) is left untouched: browsers never parse <noscript> content into the DOM when JavaScript is enabled, so a script-driven rewrite of that link can never actually run, and for JS-disabled visitors there's no ?ref= handling happening anyway (the widget itself requires JS).

Test plan

• Full hugo build completes cleanly.
• Local dev server, checked with browser-chauffeur:
  • No ?ref= — <pretix-widget> has no data-campaign attribute, page renders unchanged.
  • ?ref=ISC26-TEST — data-campaign="ISC26-TEST" is set, widget still builds.
  • ?ref=<script> (invalid) — rejected by the regex, no attribute set, no JS errors.
• Re-check on the live site after merge (this repo has no PR deploy-preview environment - it only builds to production via GitHub Actions on push to master).

Screenshots

Full page, ?ref= has no visible effect on rendering (confirmed pixel-identical across all three test cases above):