```python
"""Close out a stockroom count sheet after a day's receive and issue moves."""

import re


def closing_sheet(opening: str, moves: str) -> str:
    if not isinstance(opening, str) or not isinstance(moves, str):
        raise ValueError("closing_sheet expects two strings")

    def parse_sheet(text):
        held = {}
        if text == "":
            return held
        for part in text.split(";"):
            name, colon, count = part.partition(":")
            if colon == "":
                raise ValueError(f"sheet entry has no colon: {part}")
            if re.fullmatch(r"[a-z]+", name) is None:
                raise ValueError(f"bad item name: {part}")
            if re.fullmatch(r"0|[1-9]\d*", count) is None:
                raise ValueError(f"bad count: {part}")
            if name in held:
                raise ValueError(f"duplicate sheet entry: {name}")
            held[name] = int(count)
        return held

    def apply_moves(held, moves):
        move_parts = moves.split(";")
        for move in move_parts:
            if not move:
                continue
            name, sign, qty_str = move.partition("+")
            if not all((name, sign, qty_str)):
                raise ValueError(f"malformed move: {move}")
            if sign != "+" and sign != "-":
                raise ValueError(f"bad sign in move: {move}")
            if re.fullmatch(r"[1-9]\d*", qty_str) is None:
                raise ValueError(f"bad quantity in move: {move}")
            qty = int(qty_str)
            if sign == "+":
                if name not in held:
                    held[name] = 0
                held[name] += qty
            else:
                if name not in held:
                    raise ValueError(f"issue of unknown item: {name} {qty}")
                if held[name] < qty:
                    raise ValueError(f"issue more than on hand: {name} {qty}")
                held[name] -= qty

    held = parse_sheet(opening)
    apply_moves(held, moves)

    entries = [f"{name}:{held[name]}" for name in sorted(held) if held[name] > 0]
    return ";".join(entries)
```