```ts
/** Close out a stockroom count sheet after a day's receive and issue moves. */

function parseSheet(opening: string): Map<string, number> {
  const held = new Map<string, number>();
  if (opening === "") {
    return held;
  }
  for (const part of opening.split(";")) {
    const colon = part.indexOf(":");
    if (colon < 0) {
      throw new Error(`sheet entry has no colon: ${part}`);
    }
    const name = part.slice(0, colon);
    const count = part.slice(colon + 1);
    if (!/^[a-z]+$/.test(name)) {
      throw new Error(`bad item name: ${part}`);
    }
    if (!/^(?:0|[1-9]\d*)$/.test(count)) {
      throw new Error(`bad count: ${part}`);
    }
    if (held.has(name)) {
      throw new Error(`duplicate sheet entry: ${name}`);
    }
    held.set(name, Number(count));
  }
  return held;
}

function applyMove(sheet: Map<string, number>, move: string): void {
  const [name, qtyStr] = move.split("+").map((part) => part.trim());
  if (move.startsWith("-")) {
    name = name.replace("-", "");
   qtyStr = "-" + qtyStr;
  }
  const qty = parseInt(qtyStr, 10);
  if (isNaN(qty)) {
    throw new Error(`invalid quantity: ${move}`);
  }
  const count = sheet.get(name);
  if (count === undefined) {
    throw new Error(`issue of an item not held: ${move}`);
  }
  if (qty > count) {
    throw new Error(`issue more units than the item then holds: ${move}`);
  }
  sheet.set(name, count - qty);
}

export function closingSheet(opening: string, moves: string): string {
  if (typeof opening !== "string" || typeof moves !== "string") {
    throw new Error("closingSheet expects two strings");
  }
  const held = parseSheet(opening);
  for (const move of moves.split(";")) {
    applyMove(held, move);
  }
  const entries: string[] = [];
  for (const [name, count] of held.entries()) {
    if (count > 0) {
      entries.push(`${name}:${count}`);
    }
  }
  return entries.join(";");
}
```