rpc: add stripbip32derivs to PSBT processing RPCs #35370

This PR adds a stripbip32derivs option to both the walletprocesspsbt and descriptorprocesspsbt RPCs.

Motivation

Currently, setting bip32derivs=false only prevents the addition of new key-origin metadata. It does not remove BIP32 derivation metadata that is already present in the input PSBT. For collaborative PSBT workflows, users may want to strip this existing metadata before sharing the PSBT with counterparties.

Behavior

Setting stripbip32derivs=true removes standard key-origin fields from the returned PSBT, including global xpubs and BIP32 derivation paths.

If stripbip32derivs=true is used without explicitly setting bip32derivs, the RPC suppresses adding new key-origin metadata and strips existing standard key-origin fields.

Explicitly setting both stripbip32derivs=true and bip32derivs=true is rejected. This avoids asking the RPC to add and remove the same class of metadata in a single call.

Implementation Notes

The same option is applied to descriptorprocesspsbt because it shares the same bip32derivs behavior and can return the same class of key-origin metadata.

Following prior review feedback in #30341, the stripping functionality is implemented in the PSBT processing RPCs rather than combinepsbt.

Tests

• git diff --check origin/master..HEAD
• python -m py_compile .\test\functional\rpc_psbt.py
• python3 test/functional/rpc_psbt.py --configfile=build/test/config.ini in Docker/Ubuntu

Closes #30294.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35370.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #32857 (wallet: allow skipping script paths by Sjors)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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LLM Linter (✨ experimental)

Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

• walletprocesspsbt(psbt_with_derivs, True, "ALL", True, False) in test/functional/rpc_psbt.py
• walletprocesspsbt(psbt_with_derivs, False, "ALL", True, False) in test/functional/rpc_psbt.py
• walletprocesspsbt(psbt_with_derivs, False, "ALL", False, False) in test/functional/rpc_psbt.py
• walletprocesspsbt(psbt, True, "ALL", True, False) in test/functional/rpc_psbt.py
• walletprocesspsbt(psbt_with_derivs, False, "ALL", False, False) in test/functional/rpc_psbt.py

^{2026-05-25 13:31:39}

Approach ACK.

This looks like the correct approach (in contrast to #30341), putting strip functionality in walletprocesspsbt (and also descriptorprocesspsbt).

The option does more than stripping bip32 derivation paths and it's name should reflect that.

I'm not sure about stacking yet another bool argument. Maybe it would be better to convert the existing bip32derivs into a enum/choices argument.