Trusted native plugin panels for the content editor sidebar

[logelog]

Problem

Trusted native plugins can add full admin pages and field widgets, but they cannot place contextual UI in the saved-entry settings sidebar. A plugin that shows review status, SEO readiness, or workflow guidance must send editors to another page or rely on DOM injection.

Proposed extension

A native plugin admin entry may export contentEditorPanels:

export const contentEditorPanels: ContentEditorPanelExtension[] = [
  {
    id: "review-status",
    title: "Review status",
    collections: ["posts"],
    component: ReviewStatusPanel,
  },
];

Each component receives the saved entry, its collection, and the active locale.

Host contract

• EmDash owns the section markup, heading, sidebar placement, and accessibility.
• Panels render only for saved entries. The existing new-entry editor stays unchanged.
• The host filters disabled plugins, collection mismatches, and insufficient roles.
• Contributions use stable IDs and deterministic ordering.
• Each panel has its own error boundary and retry action, so one plugin cannot break the editor settings.
• With no applicable contributions, the existing editor markup and behavior stay unchanged.

Scope

This proposal is only for trusted React plugins loaded through a native adminEntry. Sandboxed plugins remain outside this API. Panels receive read-only saved-entry context; this change adds no content mutation API.

Content-list columns, movable editor layouts, and named replacement slots are separate proposals and are not part of this contract.

Implementation

A focused implementation is available in emdash-cms/emdash PR 2187. It addresses emdash-cms/emdash issue 2227 by letting a panel read the whole saved entry instead of a single field value. The PR includes the extension types, resolver and lifecycle filtering, panel isolation, documentation, and tests.

Would maintainers be comfortable approving this focused contract?