```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

    held = parse_sheet(opening)
    # TODO: apply the day's semicolon-separated moves to the sheet,
    # validating each one, then render only the entries still on hand.
    entries = []
    for name in sorted(held):
        if name in moves:
            move, qty = moves.split(name)
            if qty == "":
                raise ValueError(f"move has no quantity: {move}")
            if re.fullmatch(r"[1-9]\d*", qty) is None:
                raise ValueError(f"bad quantity: {move}")
            if int(qty) > held[name]:
                raise ValueError(f"issue more units than held: {name}")
            held[name] -= int(qty)
        if held[name] == 0:
            entries.append(f"{name}:0")
        else:
            entries.append(f"{name}:{held[name]}")
    return ";".join(entries)
```