Problem: `nvim_exec_autocmds({buf=...})` may temporarily switch curwin/curbuf
through `aucmd_prepbuf()`. Requested statuslines/winbars before
`aucmd_restbuf()` may erroneously see the target window as current.
Solution: Track `aucmd_prepbuf()` window-switch depth and leave statusline/winbar
redraws marked dirty until the original window is restored.