What?

Closes #72858

This PR fixes the focus state issue where individual notes and their corresponding blocks were not properly collapsing when focus moved away or when clicking outside the note. The fix ensures that expanded notes automatically collapse when:

1. Focus moves away from the note thread
2. The user interacts with elements outside the note

Why?

Previously, when a note was expanded and the user clicked outside the note (either within the panel or outside it), or when focus moved away from the note, the note's focus state (drop shadow, white background, etc.) and the corresponding block highlighting would persist incorrectly. This created a confusing user experience where notes appeared to remain selected even after the user had moved on.

This issue was reported in #72858 and affects the Notes feature in the Gutenberg editor, particularly when using the collaborative sidebar.

How?

The implementation adds two key behaviors:

1. Focus-based collapse: Enhanced the onBlur handler in the Thread component to detect when focus moves outside the thread element and automatically collapse the note by calling unselectThread().

2. Selection clearing mechanism: Added a clearSelection callback function in the Comments component that:

   • Finds the currently selected thread
   • Clears its block spotlight
   • Resets the selected thread state
   • Closes any open new note forms

Testing Instructions

1. Open a post or page in the editor.
2. Add a few blocks with notes (or create notes on existing blocks).
3. Click on a note to expand it - verify it expands and the block is highlighted.
4. Test clicking outside the note:
   • Click on empty space within the notes panel - the note should collapse and block highlighting should be removed.
   • Click on another note - the previous note should collapse and the new one should expand.
5. Test focus behavior:
   • Click on a note to expand it.
   • Click outside the note or tab away - the note should automatically collapse.
   • Verify that the block spotlight is removed when the note collapses.

Video