ISO date string (YYYY-MM-DD)
Article-type slug (e.g. breaking)
OptionalrunSuffix: stringOptional collision-suffix (e.g. run191) appended
when multiple runs share the same (date, articleType) pair
Combined slug used as the file-stem for every language variant
Build the article slug
YYYY-MM-DD-<article-type>[-<runSuffix>]. The slug is the file-stem shared by every language variant (<slug>.en.md,<slug>-<lang>.html, …).