Support hidden repeater sub-fields

[dennisklappe]

Summary

Allow repeater sub-fields to be marked hidden: true: kept in the entry data, but not rendered in the content editor.

Use case

A common pattern is storing editable site copy as { label, value, key } rows, where a template looks each text up by a stable key. Today every sub-field is rendered and editable, so editors see the raw key next to the text. Exposing it is clutter and a footgun, since renaming it silently breaks the lookup. There is no way to keep the key in the data while hiding it from editors.

Proposal

Add an optional hidden?: boolean to repeater sub-fields. A hidden sub-field is not rendered, and its value is preserved on save (item updates already spread existing fields, so the round-trip is safe).

Implementation

• PR: feat(admin): support hidden repeater sub-fields #1585 (core type + schema validator, admin RepeaterField skips hidden sub-fields, tests, changeset).

Userland plugin (works today)

While the core change is reviewed, I built a small field-widget plugin that solves the same problem in userland by rendering a json field as clean labeled text boxes and keeping the other keys untouched:

• https://github.com/dennisklappe/emdash-plugin-copydeck

It works, but a native hidden flag would be the cleaner primitive and would apply to any repeater, not just a copy list. Opening this to get maintainer feedback on the approach before the PR lands.