Module cursor 

Prompt cursor coordinate calculation.

Given prompt text, a grapheme-cluster cursor position, the body width (columns available for text), and an optional prompt indent, compute the (row, col) coordinate of the cursor within the prompt’s visual rows.

Uses unicode_width for display-width measurement so that wide characters (CJK), zero-width characters (combining marks), and emoji are handled correctly. Cursor position is expressed as a grapheme-cluster index (matching crate::input::PromptInput).

Handles:

• single-line input;
• word/char wrapping at body_width using display width, not char count;
• explicit \n newlines;
• a leading prompt indent applied to every visual row;
• multibyte and grapheme clusters.

Functions

prompt_cursor

Compute the (row, col) coordinate of the cursor in the prompt’s visual rows.

prompt_rows

Decompose prompt text into visual rows of text (without the indent) for rendering. Uses display width for wrapping so wide characters occupy the correct number of columns.