rpc: Add validation for invalid taproot signatures in analyzepsbt #33360

1. 
   jalateras commented at 0:55 am on September 11, 2025: none

   Summary

   This PR fixes issue #33320 by adding explicit validation for invalid taproot key path signatures in the analyzepsbt RPC command.

   Problem

   Currently, when a PSBT contains an invalid taproot_key_path_sig, analyzepsbt returns a confusing status of "next": "updater" instead of properly reporting the validation error. This can happen when external applications incorrectly construct PSBTs.

   Solution

   • Added validation in AnalyzePSBT to check for invalid taproot key path signatures
   • Check signature length (must be 64 or 65 bytes for valid Schnorr signatures)
   • Return clear error message when signature is invalid
   • Added test coverage in rpc_psbt.py

   Testing

   • Added functional test that verifies the error is properly reported for PSBTs with invalid taproot signatures
   • Existing tests continue to pass

   Fixes #33320

2. rpc: Add validation for invalid taproot signatures in analyzepsbt

   Previously, analyzepsbt would return a confusing "next": "updater" status
   when a PSBT contained an invalid taproot key path signature, instead of
   properly reporting the validation error.
   
   This commit adds explicit validation for taproot key path signatures:
   - Check signature length (must be 64 or 65 bytes)
   - Provide clear error message when signature is invalid
   - Add test coverage for this edge case
   
   This helps external applications that may incorrectly construct PSBTs
   get better error feedback.
   
   🤖 Generated with [Claude Code](https://claude.ai/code)
   
   Co-Authored-By: Claude <noreply@anthropic.com>

   e78d3573a0
3. DrahtBot added the label RPC/REST/ZMQ on Sep 11, 2025
4. 
   DrahtBot commented at 0:55 am on September 11, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33360.

   Reviews

   See the guideline for information on the review process. A summary of reviews will appear here.

Contributors
jalateras DrahtBot

Labels
RPC/REST/ZMQ