The copy was dropped only when a claimed drawer threw. A built-in drawing
exception (BuildDictionary, SetValue, a throwing constructor, Clone) or an
ExitGUIException escaped OnGUI with the copy alive, and the next change
committed the half-made edit.
The window now takes the copy out of _edit before drawing and puts it back
only when the document drew to the end with no drawer failing. Every
abnormal exit, ExitGUIException included, leaves the next frame to clone
afresh from the cache.
ExitGUIException is dropped too, not exempted: Unity's pickers exit on the
click that opens them and deliver the pick in a later event, which lands
on the fresh copy and commits normally.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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