```typescript

/** 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;
}

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(";")) {
    const parts = move.split("+", "-").map(p => p.trim());
    if (parts.length < 2 || parts[0] === "" || !/^[a-z]+$/.test(parts[0]) || !/[+-]\d+$/.test(parts[1])) {
      throw new Error(`malformed move: ${move}`);
    }
    const [name, qtyStr] = parts;
    const qty = Number(qtyStr);
    if (qty <= 0) {
      throw new Error(`quantity must be positive: ${move}`);
    }
    if (!held.has(name)) {
      throw new Error(`issue of item not on sheet: ${move}`);
    }
    const count = held.get(name)!;
    if (count < qty) {
      throw new Error(`issue of more units than available: ${move}`);
    }
    held.set(name, count - qty);
  }

  const entries: string[] = [];
  for (const [name, count] of [...held.entries()].sort((a, b) => a[0].localeCompare(b[0]))) {
    if (count > 0) {
      entries.push(`${name}:${count}`);
    }
  }
  return entries.length > 0 ? entries.join(";") : "";
}
```