Function media_block_rows 

pub fn media_block_rows(
    block: MediaBlockRef,
    anchor_line: u32,
    rows: u16,
    width_cols: usize,
) -> Vec<VirtualRow>

Build the virtual rows for a media block anchored below anchor_line.

The rows carry the alt text as ordinary cells, which is the whole of the TUI’s rendering: it paints what it is given and needs no media code. The GPUI peer recognises the kind and paints an image over the region instead — the BrandingBlock treatment.

rows is clamped to at least 1: a zero-row block would be invisible on both peers while still occupying a slot in the matrix, which is a bug that presents as “the image silently did nothing”.