const ASSISTANT_CHARS_PER_LINE_FALLBACK = 72;const USER_CHARS_PER_LINE_FALLBACK = 56;const LINE_HEIGHT_PX = 22;const ASSISTANT_BASE_HEIGHT_PX = 78;const USER_BASE_HEIGHT_PX = 96;const ATTACHMENTS_PER_ROW = 2;// Attachment thumbnails render with `max-h-[220px]` plus ~8px row gap.const USER_ATTACHMENT_ROW_HEIGHT_PX = 228;const USER_BUBBLE_WIDTH_RATIO = 0.8;const USER_BUBBLE_HORIZONTAL_PADDING_PX = 32;const ASSISTANT_MESSAGE_HORIZONTAL_PADDING_PX = 8;const USER_MONO_AVG_CHAR_WIDTH_PX = 8.4;const ASSISTANT_AVG_CHAR_WIDTH_PX = 7.2;const MIN_USER_CHARS_PER_LINE = 4;const MIN_ASSISTANT_CHARS_PER_LINE = 20; interface TimelineMessageHeightInput {  role: "user" | "assistant" | "system";  text: string;  attachments?: ReadonlyArray<{ id: string }>;} interface TimelineHeightEstimateLayout {  timelineWidthPx: number | null;} function estimateWrappedLineCount(text: string, charsPerLine: number): number {  if (text.length === 0) return 1;   // Avoid allocating via split for long logs; iterate once and count wrapped lines.  let lines = 0;  let currentLineLength = 0;  for (let index = 0; index < text.length; index += 1) {    if (text.charCodeAt(index) === 10) {      lines += Math.max(1, Math.ceil(currentLineLength / charsPerLine));      currentLineLength = 0;      continue;    }    currentLineLength += 1;  }   lines += Math.max(1, Math.ceil(currentLineLength / charsPerLine));  return lines;} function isFinitePositiveNumber(value: number | null | undefined): value is number {  return typeof value === "number" && Number.isFinite(value) && value > 0;} function estimateCharsPerLineForUser(timelineWidthPx: number | null): number {  if (!isFinitePositiveNumber(timelineWidthPx)) return USER_CHARS_PER_LINE_FALLBACK;  const bubbleWidthPx = timelineWidthPx * USER_BUBBLE_WIDTH_RATIO;  const textWidthPx = Math.max(bubbleWidthPx - USER_BUBBLE_HORIZONTAL_PADDING_PX, 0);  return Math.max(MIN_USER_CHARS_PER_LINE, Math.floor(textWidthPx / USER_MONO_AVG_CHAR_WIDTH_PX));} function estimateCharsPerLineForAssistant(timelineWidthPx: number | null): number {  if (!isFinitePositiveNumber(timelineWidthPx)) return ASSISTANT_CHARS_PER_LINE_FALLBACK;  const textWidthPx = Math.max(timelineWidthPx - ASSISTANT_MESSAGE_HORIZONTAL_PADDING_PX, 0);  return Math.max(    MIN_ASSISTANT_CHARS_PER_LINE,    Math.floor(textWidthPx / ASSISTANT_AVG_CHAR_WIDTH_PX),  );} export function estimateTimelineMessageHeight(  message: TimelineMessageHeightInput,  layout: TimelineHeightEstimateLayout = { timelineWidthPx: null },): number {  if (message.role === "assistant") {    const charsPerLine = estimateCharsPerLineForAssistant(layout.timelineWidthPx);    const estimatedLines = estimateWrappedLineCount(message.text, charsPerLine);    return ASSISTANT_BASE_HEIGHT_PX + estimatedLines * LINE_HEIGHT_PX;  }   if (message.role === "user") {    const charsPerLine = estimateCharsPerLineForUser(layout.timelineWidthPx);    const estimatedLines = estimateWrappedLineCount(message.text, charsPerLine);    const attachmentCount = message.attachments?.length ?? 0;    const attachmentRows = Math.ceil(attachmentCount / ATTACHMENTS_PER_ROW);    const attachmentHeight = attachmentRows * USER_ATTACHMENT_ROW_HEIGHT_PX;    return USER_BASE_HEIGHT_PX + estimatedLines * LINE_HEIGHT_PX + attachmentHeight;  }   // `system` messages are not rendered in the chat timeline, but keep a stable  // explicit branch in case they are present in timeline data.  const charsPerLine = estimateCharsPerLineForAssistant(layout.timelineWidthPx);  const estimatedLines = estimateWrappedLineCount(message.text, charsPerLine);  return ASSISTANT_BASE_HEIGHT_PX + estimatedLines * LINE_HEIGHT_PX;}