Rich text: make the child inert under the editing host to fix iOS double tap selection

[ellatrix]

What?

Fixes native iOS selection gestures (double tap to select a word) in paragraphs while the editableRoot editing host (#79105) is active, without losing native cross-block selection.

Why?

With the editing host active, double tap to select a word rarely worked on iOS. The selected paragraph was still a focusable editing area of its own (nested contenteditable="true" plus a forced tabIndex), so iOS focused it on every tap while the host code immediately moved focus back to the wrapper (a nested editable cannot retain focus once an ancestor hosts editing). That focus flip in the middle of the gesture made iOS cancel the word selection before it formed.

How?

1. Make the child inert under the host, on touch devices: while the wrapper hosts editing on a coarse pointer device, the selected block's rich text renders contenteditable="inherit" and no tabIndex, so it is editable through the host but never a focus target. Focus stays on the host for the whole gesture and iOS forms the word selection there. Fine pointer devices keep the focusable child: the desktop keyboard and selection flows are built around it (tabbable searches, focus restoration, the autocompleter, multi block selection), and unifying them behind the inert child is follow-up work.
2. "Editable" no longer means the attribute is "true": ownsSelection, the rich text selection sync, getSelectionEditableElement, and the arrow navigation tab candidate filter treat only an explicit contenteditable="false" as non-editable. Without this, all owned editing listeners went silent for the inert child and writing flow prevented every keystroke. The checks compare against the known editable values because JSDOM does not implement the contentEditable getter.
3. Keyboard flows reach the inert child: the focus-first-element search falls back to the [contenteditable="inherit"] marker when the tabbable search finds nothing, and placeCaretAtEdge places the range within an inherited editable first and then focuses its editing host, which adopts the selection (range before focus, so Safari does not asynchronously reveal a caret and scroll).

Testing Instructions

1. On an iPhone or the iOS simulator, open a post with two paragraphs and select one.
2. Double tap a word: it is selected reliably, with the selection painted on the word.
3. Tap to place the caret, type, press Enter to split, Backspace to merge.
4. Long press and drag the selection handles across both paragraphs: native cross-block selection still works.
5. On desktop, everything behaves as trunk: the gating leaves fine pointer devices on the focusable child code path.

Use of AI Tools

Written with the help of Claude Code.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XrG35JQKJBX1iNof5wtfjN

[github-actions]

Size Change: +630 B (+0.01%)

Total Size: 7.78 MB

📦 View Changed

Filename	Size	Change
build/scripts/block-editor/index.min.js	429 kB	+511 B (+0.12%)
build/scripts/dom/index.min.js	5.17 kB	+90 B (+1.77%)
build/scripts/rich-text/index.min.js	14.8 kB	+29 B (+0.2%)

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