Function render 

pub fn render<'a>(
    node: &'a TreeNode,
    ctx: RenderCtx<'a>,
) -> Element<'a, Message>

Map a TreeNode to an iced Element. Unknown types render as an empty container.

This is the immutable side of the ensure_caches/render split. All mutable cache state (text_editor Content, markdown Items, combo_box State, canvas Cache, etc.) must be pre-populated by super::ensure_caches before calling this function. render works exclusively with shared (&) references to caches, so it can run inside iced’s view() which only has &self.