Bug: Backspace does not move the caret to the previous shadow root element

[levensta]

Lexical version: 0.45 latest

Steps To Reproduce

1. Insert a shadow root element, such as CollapsibleContainer in the playground
2. Insert a paragraph of text after the shadow root element
3. Insert your cursor in the middle of the paragraph text and press Backspace

Link to code example: https://playground.lexical.dev/#doc=H4sIAAAAAAAAE9WTT2_CMAzFv8s7Z6gdMFiOHDhP4jjtkDUGIoW4cl00hPrdp5T9K9MmbTtMnCLbes8_28oR5IOyrNQpwR4hzJrfahuiF0qw94PgwcAHoUoDJ9jUxmiwZtk5hQUMQvKUFLYw0ENNsKiduI24eguDPUnTC0sDpSddviiLU7jSQ8wSdOZrgv_A-XmbimN0dRMeI11p0EiDdt_P50ldiL3b-p1oxz4bp5yJMGhe6U6wsFgy4w2gzw16XsSuKk6ay38kP7d0IZGcTcF13rdKS5_O8dsLLJxc5AX6Xz9A7Qyia3Tl9uRhy9m8vJ3dXE_G8-nYoOFWqqy7i-6wEW6T_6hGMZpMRwW6ZxU_aJVeBAAA

The current behavior

The caret gets stuck at the beginning of a paragraph and does not move to the previous element

cursor.stucks.before.shadow.root.mov

The expected behavior

The caret moves to the nearest available text-containing node, and the text after the caret is appended to it

Impact of fix

Similar behavior works in Notion and seems entirely expected. The only caveat is what happens if the last element in the shadow root is a decorator, such as an embed video. In this case, I see several options:

• The caret stops at the paragraph and does not move anywhere.
• The caret always jumps over any decorators and the text appends to the nearest available node (like in Notion)

[etrepum]

This is intentional behavior and would need an extension and config to change it.