Writing Flow: Highlighting text starting from outside does not reveal toolbar formatting options

[tyxla]

Description

When using the Top Toolbar setting in the block editor, highlighting text starting from the left side of a paragraph does not show Bold or other paragraph formatting options in the toolbar.

cc @davemart-in, who reported this issue initially.

Step-by-step reproduction instructions

1. Enable Top Toolbar in editor preferences
2. Add a paragraph block with text
3. Highlight text starting from the left or right edge of the paragraph (the padding on the left/right)
4. Observe that Bold/Italic and other paragraph formatting options do not appear in the Top Toolbar.

Screenshots, screen recording, code snippet

Screen.Recording.2026-04-08.at.12.22.36.mov

Environment info

• Gutenberg on trunk
• Chrome 146.0.7680.178
• MacOS Tahoe 26.4

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[tyxla]

I'll file a fix for this

[tyxla]

Resolved by: #77136