fix(seo): buildMediaUrl handles root-relative paths without doubling the API prefix

[abhishekshankar]

Summary

buildMediaUrl(imageRef, siteUrl) in packages/core/src/seo/index.ts currently handles two cases:

1. Absolute URL (https://...) → returned as-is
2. Anything else → treated as a bare media_id and built as ${siteUrl}/_emdash/api/media/file/${imageRef}

But the CMS SEO panel stores seo_image as a root-relative path that already includes the API prefix, e.g. /_emdash/api/media/file/01KS...svg. Branch 2 fires and produces:

https://example.com/_emdash/api/media/file//_emdash/api/media/file/01KS.svg
                                          ^^ doubled

…which 404s and breaks <meta property="og:image"> for every post that used the SEO panel to set an image.

Repro

import { getSeoMeta } from "emdash/seo";

const meta = getSeoMeta(
  { seo: { image: "/_emdash/api/media/file/01KS.svg" }, data: {} },
  { siteUrl: "https://example.com" },
);

console.log(meta.ogImage);
// → "https://example.com/_emdash/api/media/file//_emdash/api/media/file/01KS.svg"
// expected:
// → "https://example.com/_emdash/api/media/file/01KS.svg"

Fix

Add a third branch BEFORE the bare-media_id branch that detects root-relative inputs (imageRef.startsWith("/")) and joins them with the host directly — no API-prefix re-prepending.

if (imageRef.startsWith("/")) {
  return siteUrl
    ? `${siteUrl.replace(TRAILING_SLASH_RE, "")}${imageRef}`
    : imageRef;
}

Test plan

New unit tests at packages/core/tests/unit/seo/get-seo-meta.test.ts cover:

• ✅ Absolute URLs pass through unchanged
• ✅ Root-relative paths join with siteUrl without doubling the prefix
• ✅ Root-relative paths returned as-is when no siteUrl
• ✅ Bare media_id still builds the full API path
• ✅ Trailing slash on siteUrl is stripped before joining

These don't need DB setup — direct unit tests against getSeoMeta.

Bonus (separate PR if you'd like)

The same logic gets re-implemented by user code that needs to resolve media references outside of getSeoMeta (avatar URLs, JSON-LD ImageObject.url, list-page thumbnails). Those sites currently either reach for import { buildMediaUrl } from "emdash/seo" (fails — not exported) or re-implement the logic inline and drift.

Exporting buildMediaUrl would be a one-line addition:

-export { getContentSeo, getSeoMeta };
+export { buildMediaUrl, getContentSeo, getSeoMeta };

Happy to file as a follow-up.

Reference

We currently carry this fix as a patch-package patch in a downstream fork: https://github.com/abhishekshankar/abhishek-shankar.com-emdash/blob/master/patches/emdash%2B0.9.0.patch — happy to delete it once this lands.

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