```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_move(held, move):
        if move == "":
            return held
        name, qty = move.split("+")
        if name not in held:
            raise ValueError(f"issue of item not on sheet: {move}")
        if qty > held[name]:
            raise ValueError(f"issue of more units than item holds: {move}")
        held[name] += int(qty)
        return held

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