confirm-a-delivery

Confirm a delivery on a Let Me Buy storefront

mark_as_delivered takes two accounts — the store's receipts PDA and the authority — plus a receipt id. It is signed by the store, never the buyer.

The argument-name trap

The receipts PDA derives from ["receipts", store_name]. But this instruction's own arguments are named _store_name and receipt_id — with a leading underscore, because Rust marks an unused parameter that way and Anchor copies the name straight into the IDL.

So the seed points at an argument name that does not exist in the instruction that uses it. Bind the store name to _store_name on the wire and to store_name in the seed. A tool that passes the IDL's seed path through verbatim derives nothing; a tool that renames the argument to match the seed sends a field the program does not have.

This is the join an IDL loses, and it is why the recipe is carried separately.

The trap that loses orders, and it is silent

The receipts vec is capped at 20 and the account never reallocs — it is fixed at 3,681 bytes. At the cap, make_purchase calls receipts.remove(0): the oldest receipt is evicted with no error, no event and no log.

One measured store has 125 purchases and holds 20. 105 receipts are gone from chain.

The consequence for this instruction is the part to plan around:

mark_as_delivered on an evicted id SUCCEEDS AND DOES NOTHING. It scans the vec, finds nothing, and returns Ok.

So a venue with more than 20 open orders loses them from the delivery queue invisibly, and the program will keep telling you the delivery worked. Never treat a successful mark_as_delivered as proof the order was closed — read the receipt back and check was_delivered actually flipped.

If you are building a delivery queue on this program, the queue depth is 20. Hold your own record of anything beyond it; the chain will not.

Finding the receipt

Read the store's receipts account and match on the buyer, the product and the table number. The vec is sequential and there is no index, so a walk reads every row — every other row belongs to a real customer of a real storefront. Compare and discard; do not carry other people's rows anywhere.