refac: migration crash, real-database tests, site deleted during create, ruels out of the repo, lists

docs/api/article-localization.md

@@ -43,6 +43,7 @@ The headers are set on those responses only. Same-origin SPA code reads them dir
 | 409 | `slug_taken` | a `PATCH` slug used by another article of the same site and language (`X-Slug-Suggestion`) |
 | 409 | `slug_conflict` | a move would put an address that already exists at the destination (`X-Conflicting-Articles`) |
 | 409 | `story_move_required` | `PATCH site_id` on a version whose story holds several versions |
+| 409 | `target_site_deleted` | `POST /v1/article/`: the target site was deleted after it was looked up and before the article was stored; choose another site |
 | 409 | `story_busy` | the database could not lock the rows in time (lock timeout, deadlock or serialization failure); retry |
 | 422 | `invalid_language` | the tag is not a language tag |
 | 422 | `unsupported_language` | a valid tag outside the supported list |
@@ -144,7 +145,7 @@ It creates a new story with one offline version, on the default site unless the
 {"title": "Neuf", "lang": "fr", "site": "atelier"}
 ```
 
-- `site` is optional: the site key. Absent or `null`, the default site is used exactly as before. A present `site` is validated like any site key (`400` with the plain-text body `invalid_site_key` for `""` or `Bad Key!`), then looked up (`404 site_not_found` for an unknown key, a plain text body, nothing stored). Every caller who may create articles may create on every site: `content.create` is not scoped to a site.
+- `site` is optional: the site key. Absent or `null`, the default site is used exactly as before. A present `site` is validated like any site key (`400` with the plain-text body `invalid_site_key` for `""` or `Bad Key!`), then looked up (`404 site_not_found` for an unknown key, a plain text body, nothing stored). A site deleted after that lookup and before the article is stored answers `409 target_site_deleted` (plain text, nothing stored). Every caller who may create articles may create on every site: `content.create` is not scoped to a site.
 - `lang` is optional. Absent, the version gets the starting language of the chosen site; present, it is normalized and must be an enabled language of the chosen site (`422 invalid_language`, `unsupported_language`, `language_not_enabled`; `409 language_unavailable` when disabled on that site; `409 setup_required` before that site's default language is confirmed). The same tag can therefore be accepted on one site and refused on another.
 - The slug is generated from the title and made free within the chosen site and language only.
 - `site` with `story_id`, `source_article_id` or `copy` answers `400` with the body mismatch message and stores nothing. `POST /v1/article/{id}/translations` has no `site` field: the translation keeps the site of its source and an unknown `site` key in its body is ignored.