Function setCellStyleId

src/ink/screen.ts:817–839

(
  screen: Screen,
  x: number,
  y: number,
  styleId: number,
)

 * for the cell so diffEach picks up the change.
 */
export function setCellStyleId(
  screen: Screen,
  x: number,
  y: number,
  styleId: number,
): void {
  if (x < 0 || y < 0 || x >= screen.width || y >= screen.height) return
  const ci = (y * screen.width + x) << 1
  const cells = screen.cells
  const word1 = cells[ci + 1]!
  const width = word1 & WIDTH_MASK
  // Skip spacer cells — inverse on the head cell visually covers both columns
  if (width === CellWidth.SpacerTail || width === CellWidth.SpacerHead) return
  const hid = (word1 >>> HYPERLINK_SHIFT) & HYPERLINK_MASK
  cells[ci + 1] = packWord1(styleId, hid, width)
  // Expand damage so diffEach scans this cell
  const d = screen.damage
  if (d) {
    screen.damage = unionRect(d, { x, y, width: 1, height: 1 })
  } else {
    screen.damage = { x, y, width: 1, height: 1 }
  }
}

/**
 * Intern a character string via the screen's shared CharPool.