Sign-in page: a language picked before signing in is not saved as the person's own preference when they have none (save after #30157) #30399

domain:ui#3 · os-bill · session_01Utp6CbPN5UYMnBaNJPJWfG

Follow-up card the domain:ui#3 seat owes from #30338 (ruling D, claim 6653153124). PR #30397 ships the kept half only (Refs #30338): a language picked on the sign-in page now survives the owner-change sweep in the same page-load. This card is the saved half.

Observed

• A language picked on the sign-in page is dropped when someone else last used that browser, and the sign-in list differs from the signed-in one #30338 Wanted: a pick made on the sign-in page is "saved as their own preference if they have none". After fix(app-shell): keep a language picked on the sign-in page when someone else last used the browser #30397 the pick is kept in the objectui-locale slot but never written to sys_user.locale.
• The save needs the signed-in adapter write adapter.update('sys_user', id, {locale}) (the globe's door, useUserLocale.ts). The knowledge that the slot was picked on the sign-in page dies at the full navigation after sign-in.
• "Column null + slot set" on the next page-load is not a usable signal: the profile card's "use deployment default" writes locale: null and leaves the slot set, so saving the slot there would undo that choice on every boot.
• Measurement: /mnt/project-files/ui-seat3/measure-30338.md (project file) and os-dev-report 6654595947.

Ruled route (seat ruling D, 11-05)

Route B: in the sign-in page-load, when the person signs in with a pick made on that page and their sys_user.locale is unset, await the sys_user write before window.location.assign. ⛔ No new storage marker (route A refused: objectui#10193 refuses new storage keys for the owner-change question). ⛔ No fire-and-forget beside the navigation (route C races the unload).

Serial

The write lives in ui/apps/console/src/pages/auth/** (LoginPage), held by #30157 (domain:ui#4, PR #30243). Start after #30157 lands.

Blocked-by: #30157
Refs: #30338