Function cursor_shape 

pub fn cursor_shape(mode: Mode) -> CursorShape

The CursorShape the GPU backend should draw for mode. Derived from the single typed Mode::cursor_shape mapping shared with the TUI backend — so the GPU cursor (once it gains a dedicated glyph; today the buffer text carries the caret) renders the same shape the TUI does for any given mode. Exposed now so the shape is a typed value at the GPU layer, not a renderer-local literal later.