Function forget_subtree_buffer

pub fn forget_subtree_buffer(root: NodeRef) -> bool

Drop the cached subtree buffer for root, freeing its render surface and image snapshot. Call this when a plane is retired (e.g. its window closed) so its buffer doesn’t linger in the cache for the lifetime of the process — the cache is only ever populated on render and is not otherwise evicted. Returns true if an entry was present. Must run on the render thread (same thread that called render_subtree_to_buffer).