Editor initialization causes duplicated fullscreen button in wiki editor

Description

The wiki editor toolbar sometimes displays duplicated fullscreen buttons.
The behavior is non-deterministic and appears to be caused by a race condition during editor initialization, as it changes simply by reloading the same edit page.

The issue can be reproduced reliably by repeatedly reloading the editor page.

Steps to Reproduce

• Create a new sub-wiki using the standard flavor
• Open any page in wiki edit mode (/bin/edit)
• Reload the editor page multiple times
• Observe the editor toolbar and fullscreen behavior

Observed Results

• On many page loads, two fullscreen buttons are displayed in the editor toolbar
• On other page loads, only one fullscreen button is shown
• Reloading the same page toggles between both states
• When entering fullscreen mode, a duplicated fullscreen edit button remains visible in the fullscreen overlay (“fullscreen mirror”)

Case 1 – duplicated fullscreen button

Selector:

#xwikieditcontentinner > div.leftmenu2 > img.fullScreenEditButton

→ Two instances present simultaneously

Case 2 – fullscreen mode

Selectors:

#xwikieditcontentinner > div.leftmenu2 > img.fullScreenEditButton
#xwikieditcontentinner > div.leftmenu2 > img.fullScreenCloseButton

→ The fullscreen edit button remains visible next to the close button

Expected Results

• Exactly one fullscreen button should be displayed at all times
• When entering fullscreen mode, only the close button should be visible
• Editor initialization should be deterministic, independent of reload timing

Additional Notes

• Issue persists after hard refresh
• Observed only in the wiki editor, not in the object editor