Bip370 PSBTv2 support

[jvgelder]

To get #2269 working, we’ll need BIP370 (PSBTv2) first, since Silent Payments fields depend on it.

I’ve started an early implementation here:
https://github.com/jvgelder/bip370

It’s not finished yet, but I’d really appreciate early feedback on direction before going further.

Specifically:

• API design – What interface would you prefer? (e.g. batch updates, parity with current bitcoinjs PSBT API)
• Validation behavior – How strict should it be? Preserve unknown fields?
• Scope – Should it verify derivation paths / script correctness, or stay purely structural?

Notes:

• Mostly aligned with BIP174 patterns, but with stricter validation and explicit errors.
• No PSBTv0 support (could be added if needed).

Would love thoughts on whether this direction makes sense.

[jasonandjay]

Maintainer triage: treating this as the canonical thread for PSBTv2 (BIP370) planning/implementation.

Action items:

• parser/serializer compatibility
• validation rules + test vectors
• migration/backward-compat notes

Related older request will be closed as duplicate to keep discussion in one place.

[claytonlin1110]

Can i take this feature?

[jvgelder]

I committed my progress if you have some feedback let me know!
Especially looking for what should be in scope of the lib and what we should handle else where for example in bitcoinjs

[RyanBetz]

I ran a repo-mapping tool on this and it points to the Psbt class in ts_src/psbt.ts as the core boundary where parsing, validation, and API behavior all converge.

It seems like PSBTv2 would fit best by extending that layer directly, rather than introducing separate flows, so it stays consistent with the current API and validation model.