[DevTools] Clear element inspection if host element not owned by any renderer is selected

[everettbu]

Mirror of facebook/react#35504
Original author: eps1lon

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Stacked on react/react#35503

If you click outside a React root in the Elements panel, we want to give eedback that no selection is possible so we clear the selection. Otherwise clicking outside a React root is indistinguishable from clicking a different host node that leads to the same selected React element due to Component filters.

Test plan

1. Open a document where not all DOM nodes are rendered by React e.g. https://react.new/
2. Select a DOM node owned by React
3. Select a DOM node not owned by React

CleanShot.2026-01-13.at.19.22.50.mp4

1. Open a document where not all DOM nodes are rendered by React e.g. https://react.new/
2. Open Components panel
3. inspect element
4. Open Elements panel (should clear inspection since the selected host node is not owned by React)

CleanShot.2026-01-13.at.20.02.00.mp4

[greptile-apps]

Greptile Summary

This PR improves the DevTools' element inspection behavior by enabling clear visual feedback when selecting non-React elements. The core change allows the extension to send null through the selection pipeline when users click on DOM nodes not owned by React, which clears the Components panel selection and distinguishes this state from selecting different React elements.

Key Changes:

• Backend now sends null to the bridge when selectNode() is called with a non-React element
• Store properly handles null selections and emits events to update UI state
• Frontend receives null selections and clears inspection in the Components panel
• Type system updated across bridge, store, and components to support nullable element IDs
• Extension syncs selection when Elements panel is opened via new syncSelectionFromBuiltinElementsPanel message
• Removed unused editor pane visibility event emitters that had no listeners

The implementation maintains backward compatibility while adding the new null-selection behavior. All event handlers and reducers properly support the null case.

Confidence Score: 5/5

• This PR is safe to merge with no identified issues. Type system changes are consistent across all modules, logic for null selection handling is correct, and removed code had no active consumers.
• All changes follow a coherent pattern: extending type definitions to support null, updating event handlers to accept and propagate null values, and ensuring the UI state resets when non-React elements are selected. The early-return logic in store.js correctly forces event emission when elementId is null, preventing false deduplication. Removal of unused event emitters is safe as no other code depends on them. The extension's new syncSelection call properly triggers state synchronization. No logical errors, type mismatches, or security concerns were identified."
• No files require special attention

[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.