wx 3.3.2 delivers webview script messages synchronously inside the native
callback on GTK and macOS, so script plugins run with the plugins-dialog
webview's signal/delegate frame on the stack. Creating and presenting the
orca.host.ui window from there crashed on Linux at Raise() --
gtk_window_present while GTK's deferred show was still in flight.
Defer the whole window creation to a CallAfter with a pre-bound registry
handle (post/close stay FIFO-safe, teardown races become a no-op), and
drop Raise() plus the show_modeless_dialog wrapper: Show() already
activates and fronts a new window on every platform.