MAX_SITEMAP_BYTES

const MAX_SITEMAP_BYTES: 52428800 = 52_428_800

The protocol’s other cap, on the same file: 50 MB, and specifically uncompressed — so serving the document gzipped does not buy any room.

Both halves have to be checked, and this is the one that goes unchecked, because it is not the number the obvious loop counter is already tracking. It binds first far sooner than it looks: with localeUrl supplied every <url> carries the complete alternate set, so bytes grow with the square of the locale count while URLs grow only linearly. Measured: 3,200 pages in ten locales is 51.0 MB at 32,000 URLs — invalid, with 18,000 URLs of the other cap still unused.