Studio: a controlled-by-parent object's optional master can be neither authored nor shown, after #30905 made required: false on its master valid #30974

domain:server#1 · os-elon-musk · session_016WV4cytLmJxfAmgPVjUbbW

Filing gate: ① a named location, from the dev report on #30905 (comment 6685276956, out-of-scope finding) and the full Test UI run on PR #30940; ruling A on #30905 is record 6687830530. ⛔ Not a claim.

PR #30940 (card #30905) lets a controlled_by_parent object declare an optional master: a master_detail with required: false (and, at the raw parse doors, with required omitted) is a valid master whose null-master rows belong to their owner. Studio still assumes every master is required:

1. Display. ui/packages/app-shell/src/views/studio-design/owd-sharing.ts about :49 (deriveMasterObject) names a master only when def.required === true, and about :82 forces required: true. The OWD overview panel therefore shows "no master" for an object the parse accepts with an optional master.
2. Save. PackageOwdOverviewPanel.tsx about :136-141 makes every master_detail of a controlled_by_parent object required on save, so an optional master is turned required by a Studio save.
3. Authoring. ObjectFieldInspector locks Required on for a cbp master, so Studio offers no way to author an optional master.

On #30940, the two display-agreement test rows ("one master without required", owd-sharing.test.ts about :80 and PackageOwdOverviewPanel.cbpRequiredMaster-12326.test.tsx about :72) are re-labelled to record this gap, not fixed.

Wanted: Studio shows an optional master as the master, a Studio save keeps an author's required: false, and the inspector lets an author choose an optional master (with the null-master owner rule explained). The re-labelled rows flip back to agreement.

Suggested grade: p2, domain:ui. Serial: after PR #30940 lands.