Builds redirect URL for 301 redirects from cached post data.

Builds redirect URL when we only have slug data (no full post struct).

Finds the latest version directory in a versioned post structure.

Scans filesystem to find a post with matching url_slug or previous_url_slugs.

Returns:

• {:current, internal_slug} - found as current url_slug
• {:previous, internal_slug, current_url_slug} - found in previous_url_slugs (for redirect)
• {:error, reason} - not found

Reads url_slug and previous_url_slugs from a post's language file metadata.

Resolves URL slug to internal slug using cache.

Returns:

• {:redirect, url} for 301 redirect to new URL
• {:ok, identifier} for resolved internal slug
• :passthrough for direct use

Filesystem fallback for URL slug resolution when cache is unavailable. Also handles 301 redirects for previous_url_slugs.

Resolves a URL slug to the internal directory slug. Used by versioned URL handler and other places that need the internal slug.