```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 applyMoves(held: Map<string, number>, moves: string): void {
  const moveParts = moves.split(";");
  for (const move of moveParts) {
    if (move === "") {
      continue;
    }
    const [name, qtyStr] = move.split(/([-+])(\d+)/);
    const quantity = parseInt(qtyStr, 10);
    if (isNaN(quantity) || quantity <= 0) {
      throw new Error(`bad move: ${move}`);
    }
    if (!held.has(name)) {
      throw new Error(`issue of unknown item: ${name}`);
    }
    const currentCount = held.get(name)!;
    if ((move[0] === '+' && currentCount > Number.MAX_SAFE_INTEGER - quantity) ||
        (move[0] === '-' && currentCount < quantity)) {
      throw new Error(`insufficient stock for move: ${move}`);
    }
    held.set(name, move[0] === '+' ? currentCount + quantity : currentCount - quantity);
  }
}

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);
  applyMoves(held, moves);
  const entries: string[] = [];
  for (const name of [...held.keys()].sort()) {
    if (held.get(name)! > 0) {
      entries.push(`${name}:${held.get(name)}`);
    }
  }
  return entries.join(";");
}
```