Type Alias InlayOffset 

pub type InlayOffset = (u32, u32);

Inlay-hint position record. (orig_byte, char_width):

• orig_byte — utf-8 byte offset INTO THE ORIGINAL (pre-splice) line where the inlay was inserted.
• char_width — number of cells the inlay occupies in the spliced row.

Overlays (cursor, selection, diagnostic underline) take byte positions in the source rope. To map a source byte → cell column, the overlay walker scans this list and accumulates char_width for every entry with orig_byte ≤ target. The representation mirrors the TUI’s existing inlay offset arrays so S3’s cutover is a structural swap, not a logic change.