Function try_with_tree 

pub fn try_with_tree<R>(f: impl FnOnce(&mut dyn TreeOps) -> R) -> Option<R>

Like with_tree, but returns None instead of panicking when the tree can’t be entered: already borrowed, or not installed yet. A snapshot (TreeOps::snapshot) holds the borrow while the backend draws the window synchronously, and that draw can re-enter Day through a native callback — e.g. a lazy list’s viewForRow/connect_bind/cellForRow firing during cacheDisplayInRect. And platform style callbacks can fire before install_tree — e.g. GTK’s StyleManager emits a dark notify while startup applies a forced DAY_THEME scheme, before activate mounts the tree; a panic there unwinds into a C signal trampoline and aborts the process. Such callbacks use this and simply skip their work; the next real layout (or the signal’s first post-mount read) catches up.