Function SpliceOverlay

internal/app/render.go:366–386

SpliceOverlay splices `overlay` onto `bg` at visual cell position (x, y). Both strings are newline-separated; ANSI CSI escapes are preserved. Style state active at the cut point is re-emitted before the suffix so chars just past the overlay keep their original styling (otherwise they'd render in ter

(bg, overlay string, x, y int)

// the suffix so chars just past the overlay keep their original styling
// (otherwise they'd render in terminal default, often appearing white).
func SpliceOverlay(bg, overlay string, x, y int) string {
	bgLines := splitLines(bg)
	ovLines := splitLines(overlay)
	const reset = "\x1b[0m"
	for i, ov := range ovLines {
		row := y + i
		if row < 0 || row >= len(bgLines) {
			continue
		}
		ovW := visibleWidth(ov)
		prefix, rest := splitAtVisual(bgLines[row], x)
		_, suffix := splitAtVisual(rest, ovW)
		// Find style that was active at the position AFTER the overlay.
		styleAfter := effectiveStyleAt(bgLines[row], x+ovW)
		if styleAfter == reset {
			styleAfter = ""
		}
		bgLines[row] = prefix + reset + ov + reset + styleAfter + suffix
	}
	return joinLines(bgLines)
}

func splitLines(s string) []string {
	out := []string{}