stacks: the box converts a PostgreSQL major as a guarded-update step (09 6.4 part 10, decisions 35/37/38)

A step whose ladder entry carries engine_conversion {service, engine, from, to}
converts the database: the old engine alone, the check (owners, roles,
extensions, per-table row counts), pg_dumpall validated by its completion line,
the volume emptied only after the undo copy's marker is validated again, the new
engine alone, the load with ON_ERROR_STOP, the check again + PG_VERSION. Any
failure goes to the existing undo; a restart during converting is undone.
A PostgreSQL major move without the mark is refused before anything moves.
The old datadir's copy is kept until a backup is proven after the conversion.
17 tests, 9 red-proofs (audits/night-2026-09-26/B/).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/i18n/locales/en.json

@@ -2414,5 +2414,8 @@
   "settings.app_update_save_error": "The setting could not be saved. Try again.",
   "app_info.auto_update_done": "Automatic update at %s — done.",
   "backup.tier.no_space": "The full system backup does not fit: it needs %s and %s is free. Keeping fewer old backups, or a bigger disk, fixes it.",
-  "backup.tier.no_space_unknown": "The full system backup does not fit on the disk. Keeping fewer old backups, or a bigger disk, fixes it."
+  "backup.tier.no_space_unknown": "The full system backup does not fit on the disk. Keeping fewer old backups, or a bigger disk, fixes it.",
+  "update.phase.converting": "Converting the database",
+  "err.stacks.update_convert_space": "Converting the database of %s needs %s of free space, and only %s is free. Nothing changed.",
+  "err.stacks.update_engine_no_test": "This step would move the main version of the database of %s, but it has no test. Nothing changed."
 }

controller/internal/i18n/locales/hu.json

@@ -2402,5 +2402,8 @@
   "settings.app_update_save_error": "A beállítást nem sikerült elmenteni. Próbáld újra.",
   "app_info.auto_update_done": "Automatikus frissítés %s-kor — sikeres.",
   "backup.tier.no_space": "A teljes rendszermentés nem fér el: %s kell, %s szabad. Kevesebb régi mentés megtartása vagy nagyobb lemez segít.",
-  "backup.tier.no_space_unknown": "A teljes rendszermentés nem fér el a lemezen. Kevesebb régi mentés megtartása vagy nagyobb lemez segít."
+  "backup.tier.no_space_unknown": "A teljes rendszermentés nem fér el a lemezen. Kevesebb régi mentés megtartása vagy nagyobb lemez segít.",
+  "update.phase.converting": "Adatbázis átalakítása",
+  "err.stacks.update_convert_space": "A(z) %s adatbázisának átalakításához %s szabad hely kell, de csak %s van. Nem változott semmi.",
+  "err.stacks.update_engine_no_test": "Ez a lépés a(z) %s adatbázisának fő verzióját váltaná, de nincs róla próba. Nem változott semmi."
 }