Fix the checkout stock holds before the sale goes live

Checkout holds stock while a customer pays. Last sale it sold more lamps than the shelf had.

Your task

Fix Reservations so it honors its contract. The assistant may help, and it may be wrong more than once.

• available(sku) is the stock minus what live holds have on that sku
• reserve fails and changes nothing when fewer than qty are available
• an order has at most one hold, and its own current hold never counts against it
• commit sells a live hold and removes it; an expired or unknown hold returns False
• release of an unknown order does nothing
• leave run_ops alone; it is what the tests call

Hidden tests run at submit. Your prompts, runs and edits are the trace the critique reads.