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Evidence — intro hero banner applies relative_url exactly once (issue #293)

_includes/content/intro.html resolves the banner image into preview_path (lines 27–41), applying relative_url during assignment in every relative branch. The pre-fix point of use then piped it through relative_url again:

background: …, url('{{ preview_path | relative_url }}') no-repeat center center / cover;

relative_url unconditionally prepends site.baseurl, so any project site (non-empty baseurl, e.g. GitHub Pages at /reponame/) rendered the baseurl segment twice — url('/reponame/reponame/assets/…') → 404 — and every intro hero lost its background image, leaving only the dark gradient. Absolute preview URLs were mangled too (/reponame/https:/cdn…). The fix drops the redundant filter at the point of use.

How this evidence was produced

The include renders server-side, so both states are real Jekyll builds at --baseurl /zer0-mistakes, served statically: BEFORE with intro.html reverted to the PR's merge-base, AFTER at the PR head — a faithful diff of the real code change, driven by ../../intro-banner-baseurl-evidence.mjs (exact commands in its header).

What each file shows

Both preview-resolution branches a project site exercises:

  • 01-faq.png — /faq/ (the site.info_banner fallback branch). BEFORE: background URL /zer0-mistakes/zer0-mistakes/assets/images/info-banner-mountain-wizard.png → 404, hero is a flat gradient. AFTER: single prefix → 200, the banner image renders.
  • 02-graph.png — /docs/obsidian/graph/ (a page.preview without the /assets prefix — the auto-prefix branch). Same 404 → 200 flip.
  • metrics.json — the measured background-image URL and its HTTP status per page and state.

Measured before → after (from metrics.json)

Page Background URL (before) Status Background URL (after) Status
/faq/ /zer0-mistakes/zer0-mistakes/assets/images/info-banner-mountain-wizard.png 404 /zer0-mistakes/assets/images/info-banner-mountain-wizard.png 200
/docs/obsidian/graph/ /zer0-mistakes/zer0-mistakes/assets/images/previews/obsidian-graph-view.png 404 /zer0-mistakes/assets/images/previews/obsidian-graph-view.png 200

At baseurl "" (local dev, user/org Pages sites) the double application is a no-op — which is why the bug never showed on the theme's own site.

Regression test: ../../core/styling.spec.js ("Intro hero banner (issue #293)", smoke tier) — on both branches' routes, the rendered .bd-intro background-image URL must resolve 200.