Wails v3 alpha's setMenuItemBitmap on darwin calls NSMenuItem.setImage
from whichever thread invokes SetBitmap — unlike the sibling setters
for label/disabled/hidden/checked, which dispatch_sync onto the main
queue. The off-thread AppKit call doesn't redraw, so the coloured
status dot stayed stale until the user closed and reopened the menu.
Force a tray.SetMenu rebuild after updating the bitmap; the rebuild
runs processMenu inside InvokeSync, which applies the bitmap to a fresh
NSMenuItem on the main thread and macOS picks it up immediately.
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