Function graphemeWidth

packages/pi-tui/src/utils.ts:167–211

* Calculate the terminal width of a single grapheme cluster. * Based on code from the string-width library, but includes a possible-emoji * check to avoid running the RGI_Emoji regex unnecessarily.

(segment: string)

 * check to avoid running the RGI_Emoji regex unnecessarily.
 */
function graphemeWidth(segment: string): number {
	if (segment === "\t") {
		return 3;
	}

	// Zero-width clusters
	if (zeroWidthRegex.test(segment)) {
		return 0;
	}

	// Emoji check with pre-filter
	if (couldBeEmoji(segment) && rgiEmojiRegex.test(segment)) {
		return 2;
	}

	// Get base visible codepoint
	const base = segment.replace(leadingNonPrintingRegex, "");
	const cp = base.codePointAt(0);
	if (cp === undefined) {
		return 0;
	}

	// Regional indicator symbols (U+1F1E6..U+1F1FF) are often rendered as
	// full-width emoji in terminals, even when isolated during streaming.
	// Keep width conservative (2) to avoid terminal auto-wrap drift artifacts.
	if (cp >= 0x1f1e6 && cp <= 0x1f1ff) {
		return 2;
	}

	let width = eastAsianWidth(cp);

	// Trailing halfwidth/fullwidth forms and AM vowels that segment with a base.
	if (segment.length > 1) {
		for (const char of segment.slice(1)) {
			const c = char.codePointAt(0)!;
			if (c >= 0xff00 && c <= 0xffef) {
				width += eastAsianWidth(c);
			} else if (c === 0x0e33 || c === 0x0eb3) {
				width += 1;
			}
		}
	}

	return width;
}

/**
 * Calculate the visible width of a string in terminal columns.