The remembered window placement restored invisible when its monitor was
gone (undocked laptop, powered-off TV), briefly flashed a blank window at
the restored spot before the first Flutter frame, and could lose the
maximized state: the exit path hides the window before a multi-second
teardown, so a debounced save landing in that gap recorded SW_HIDE, and a
window closed while minimized-from-maximized restored as a normal window.
Validate the saved rect against current monitors and keep only the size on
a miss, apply the placement with SW_HIDE so the first-frame callback stays
the single show, skip persisting while the window is hidden, and honor
WPF_RESTORETOMAXIMIZED when deciding to relaunch maximized.
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