payjoin
audit test coverage for spec compliance
it appears not everything BIP 77 specifies was implemented correctly, see #843
now that the spec is merged, we should make a list of requirements to check for in the spec, add links to the relevant sections from doc comments in the corresponding tests where they exist, and open issues for spec requirements lacking coverage
In adding some coverage in #928 spacebear found that our spec has perhaps an unclear directive on what to do in the case of a malicious modification of the pjos param in backwards-compatible receivers. https://github.com/payjoin/rust-payjoin/blob/0aa150915fb41aa58f1073c6e21615df356662f4/payjoin/src/core/receive/v2/mod.rs#L398-L422 We have already had some discussion https://github.com/payjoin/rust-payjoin/pull/928#discussion_r2259548275 about whether we should continue to modify the pjos param or error if we found that it has changed.
