Bound the sponsored priority fee instead of the compute unit price

[squadgazzz]

Description

The funder pays the transaction fee on a sponsored order, and part of that fee is the priority fee the client chooses. So a placement decides how much of the funder's balance it spends, and POST /api/v1/orders is public.

The priority fee is compute unit price * compute unit limit. Today only the price is capped, which leaves the product free: a price comfortably under the cap, paired with the maximum limit, still costs the funder 0.0014 SOL per order. The number worth bounding is the fee itself, so that is what this bounds.

It comes from config because congestion is not predictable from code and raising the ceiling should not need a release. The default of 100000 lamports is two cents at 200 dollars per SOL, and close to a thousand times what a real sponsored creation pays: the last one on chain paid 113 lamports of priority fee, S9LaNbET8j53nUB1FP3JJAHi..., total fee 10113 against a 10000 base for two signatures.

Changes

• [sponsoring] max-priority-fee-lamports, default 100000, replaces the compute unit price cap
• The price and the limit are read together and the implied fee is checked once. A transaction declaring no limit is priced at the network's compute ceiling, since it may consume up to it
• A repeated compute-budget instruction is rejected, since the runtime rejects it too and the value we read would never be the one that runs

How to test

New unit tests and an updated integration test. The integration case pairs a price below the old cap with a limit that breaks the new ceiling, so the current code accepts it and this one refuses it.

[tilacog]

I think this might be off.

[tilacog]

100,000 lamports = 0.0001 SOL = $0.02 at $200/SOL.

[squadgazzz]

Checked a real one on chain, https://explorer.solana.com/tx/S9LaNbET8j53nUB1FP3JJAHib8QK2p7KtrKYAVctaTTxXJVqXyGqAfxQfUTmcPrVaMj9XoyyxnvVsgvQrNnFRfn pays 113 lamports of priority fee (total 10113, base 10000 for two signatures).

So the default is around 1000x today's traffic, not what I wrote in the comment. Kept 100000 though, since wallets raise the price 10x to 100x under congestion, and I would rather overpay 2 cents than reject real placements on a bad day. Comment fixed.