fix(combine_psbt): Propagate Psbt::combine errors

[tvpeter]

Description

wallet ... combine_psbt discarded the result of every Psbt::combine call, so two BIP174-incompatible PSBTs (different unsigned transactions) produced exit code 0 and a PSBT that was silently missing the other PSBT's inputs and signatures.

This PR propagates the error with ?. BDKCliError already has a #[from] impl for bitcoin::psbt::Error, so no new error variant was needed.

Fixes #323

Changelog notice

• Fixed combine_psbt to fail when PSBTs cannot be combined instead of silently dropping them

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.78%. Comparing base (5afbc8a) to head (682e414).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #324   +/-   ##
=======================================
  Coverage   57.78%   57.78%           
=======================================
  Files          22       22           
  Lines        3733     3733           
=======================================
  Hits         2157     2157           
  Misses       1576     1576           

Flag	Coverage Δ
rust	57.78% <100.00%> (ø)

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[vadim-anfv]

tACK 682e414

Reproduced offline with two PSBTs spending the same dummy input but with different outputs, so their unsigned txs differ:

A=$(bitcoin-cli createpsbt '[{"txid":"1111111111111111111111111111111111111111111111111111111111111111","vout":0}]' '[{"data":"aa"}]')
B=$(bitcoin-cli createpsbt '[{"txid":"1111111111111111111111111111111111111111111111111111111111111111","vout":0}]' '[{"data":"bb"}]')
echo $A; echo $B
cHNidP8BAD8CAAAAARERERERERERERERERERERERERERERERERERERERERERAAAAAAD9////AQAAAAAAAAAAA2oBqgAAAAAAAAA=
cHNidP8BAD8CAAAAARERERERERERERERERERERERERERERERERERERERERERAAAAAAD9////AQAAAAAAAAAAA2oBuwAAAAAAAAA=

D=$(mktemp -d)
DESC=$(cargo run -q -- -n regtest -d $D descriptor --type tr | jq -r .private_descriptors.external)
cargo run -q -- -n regtest -d $D wallet -w demo config -e "$DESC" --database-type sqlite

master: A B exits 0 and returns B, A is silently dropped.

$ cargo run -q -- -n regtest -d $D wallet -w demo combine_psbt $A $B; echo "exit=$?"
{
  "psbt": "cHNidP8BAD8CAAAAARERERERERERERERERERERERERERERERERERERERERERAAAAAAD9////AQAAAAAAAAAAA2oBuwAAAAAAAAA=",
  "is_finalized": false
}
exit=0
$ cargo run -q -- -n regtest -d $D wallet -w demo combine_psbt $A $A; echo "exit=$?"
{
  "psbt": "cHNidP8BAD8CAAAAARERERERERERERERERERERERERERERERERERERERERERAAAAAAD9////AQAAAAAAAAAAA2oBqgAAAAAAAAA=",
  "is_finalized": false
}
exit=0

this branch: A B fails, A A unchanged.

$ cargo run -q -- -n regtest -d $D wallet -w demo combine_psbt $A $B; echo "exit=$?"
Error: PsbtError: different unsigned transaction: expected 26defa6e8fa255cd46eac60b7a3f9e415515297498da7cecdffdd8bc818aa37a, actual 1a67d0770fe1ffa6d1d745fe12aee522cdb44985c6aee69ebe15ed80caa225ae
exit=1
$ cargo run -q -- -n regtest -d $D wallet -w demo combine_psbt $A $A; echo "exit=$?"
{
  "psbt": "cHNidP8BAD8CAAAAARERERERERERERERERERERERERERERERERERERERERERAAAAAAD9////AQAAAAAAAAAAA2oBqgAAAAAAAAA=",
  "is_finalized": false
}
exit=0