refac: article reads, story delete, no leaks, stored SEO status, rate limit, cleanup (%site%, article repo split, old lang repos, one default per site rule to domain)

docs/api/site-languages.md

@@ -73,7 +73,7 @@ Checks run in this order:
 | 7 | 409 | `language_in_use` | a removed language still has an article, draft, offline, online or soft-deleted (the display count `version_count` stays non-deleted only) |
 | any | 409 | `languages_changed` | the database could not lock the site in time because another change is running (lock contention); nothing is applied, reload and retry |
 
-Entries are checked in list order for step 4. A rejected request changes nothing. Disabling a language never touches its articles, and no article changes `lang`, status or publication. A `social_locale` is stored as `language_REGION` (`fr_fr` becomes `fr_FR`). The language part rule only compares with the tag; matching `Site.Locale` is deferred to slice 6.
+Entries are checked in list order for step 4. A rejected request changes nothing. Disabling a language never touches its articles, and no article changes `lang`, status or publication. A site always has exactly one default language: the rows are planned with one default and checked again before they are written. Changing the default language re-evaluates the stored SEO status of every article of the site, because the site `default_description` only counts for the default language (see [SEO status and suggestions](articles.md#seo-status-and-suggestions)). A `social_locale` is stored as `language_REGION` (`fr_fr` becomes `fr_FR`). The language part rule only compares with the tag; matching `Site.Locale` is deferred to slice 6.
 
 ## First-time language setup