libwinevbs's __LIBWINEVBS__ build of Global_MsgBox() only logged the
prompt text and never set a return value, since it has no host UI to
show a dialog through. Any table script that branches on
MsgBox(...) = vbYes (a common pattern - e.g. core.vbs's own trough
ball-count dialog) always took the "no" branch, since the result
stayed at its zero-initialized default.
Adds a msgbox callback to libwinevbs_callbacks_t, wired on the
vpinball-wasm side to a real window.confirm()/alert() call. Both are
synchronous browser APIs that block JS execution and return a value
immediately, matching what VBScript's MsgBox() needs (its result is
used by the calling statement right away) - the only way to answer it
asynchronously would require Asyncify or a busy-wait poll loop, which
this project has deliberately avoided elsewhere.
Confirmed fixed by hands-on testing: a table's ball-count confirm
dialog now correctly returns Yes/No based on the user's click, instead
of always silently taking the "no" branch.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
