The mega backend keeps the whole account as an in-memory tree which go-mega
reconciles asynchronously from the server's event stream. After an upload,
delete or move, the optimistic local update could be undone moments later when
go-mega replayed the corresponding server event, re-adding a node to its parent.
In a long-running process such as mount or serve this showed up as a deleted
file lingering in directory listings (a "ghost") until the next event poll, or
reappearing after a move.
Wait for the server to confirm uploads, deletes and moves so the in-memory tree
is settled before returning, matching what Rmdir and Purge already do. The move
wait was also previously started after the server-side move so only the rename
was covered.
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