Send one actionable message
Include the item, quantity, and whether it can wait. “One lemon if you're still near produce; otherwise next trip” leaves the shopper a choice. “Forgot the lemon!” leaves them wondering whether they must turn around, whether a bottle of juice works, or whether dinner now depends on the purchase.
Wait for a real handoff
The shopper can confirm if they can still add it. Until then, keep the request pending rather than assuming it is in the basket. When late additions become common, set a brief list check before departure so the trip doesn't depend on watching messages.
Mark the request pending until the shopper confirms. If they respond “already at checkout,” return the lemon to the next trip or choose a different ingredient for tonight. A delivered message or check mark on a phone does not tell you that the shopper picked up the item.
Set a practical boundary for frequent additions
Review the list briefly before the shopper leaves and agree when ordinary additions stop. If something genuinely urgent is missing afterward, explain the consequence and ask whether the shopper can help. Preserve their option to decline when they have left the shop, have limited carrying space, or need to reach another commitment.