SOP: Split an oversized sitemap into an index

Run this when one sitemap crosses either hard limit.

Step 1 — Check the two ceilings:
— ✅ Under 50,000 URLs per file
— ✅ Under 50 MB uncompressed per file (whichever hits first)

Step 2 — Shard by content type, not alphabetically. Group: products, categories, blog, static. Easier to debug coverage per shard.

Step 3 — Create sitemap-index.xml referencing each child by full absolute URL (https, not relative).

Step 4 — Cap the index itself at 50,000 child sitemaps.

Step 5 — Submit ONLY the index in Google Search Console. Never submit children individually too.

Step 6 — Delete the old monolithic file and 301 its URL to the index.

Definition of done: index returns 200, each child returns 200, GSC shows one parent reading N children with zero parse errors.