[ValeraFinebits]

Closes #195

Fix weight prediction not supported when a store contributes a Taproot UTXO to async Payjoin, reported during Bull Bitcoin testing against test/v0.3.2-alpha.rc2.

• Use the typed NewP2trKeyspend and NewP2wpkh FFI constructors.
• Add regression coverage with a P2WPKH sender and one confirmed BIP86 receiver UTXO.
• Verify that the confirmed payment spends the exact receiver outpoint with a 64-byte signature and 230 WU input weight, settles the invoice correctly, and removes the receiver session.

Local validation on Windows: 4 adapter unit tests and both SegWit and Taproot regtest payment tests pass (6 passed, 0 failed, 0 skipped). Release build, formatting, and git diff --check pass.

Pins rust-payjoin to c20d01d4edb9aa36e93ce91f99153ad6f8188b33 from rust-payjoin#1959. Coordinated with rust-payjoin#1955.

[Copilot]

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Copilot review overview

3 open findings

• The PR title indicates a production fix (\"fix: Fix Taproot receiver input handling\"), but the… · New
• The weight calculation here is fragile and may be incorrect depending on what NBitcoin includes in… · New
• The positional boolean argument (..., true, ...) makes the test harder to read/maintain because… · New

What changed in this PR

Adds an integration regression test to reproduce/guard the Taproot receiver-input Payjoin failure, and updates test helpers to support initializing wallets with Taproot derivation schemes.

Changes:

• Extend Payjoin integration test helpers to allow selecting ScriptPubKeyType (defaulting to Segwit).
• Add an integration test that funds the receiver with a BIP86 Taproot UTXO and asserts expected witness/signature/weight characteristics.

File	Description
BTCPayServer.Plugins.Payjoin.IntegrationTests/​TestUtils/​PayjoinAccountTestHelper.cs	Adds a scriptPubKeyType parameter so tests can initialize merchant wallets as Taproot (BIP86) instead of Segwit.
BTCPayServer.Plugins.Payjoin.IntegrationTests/​PayjoinPluginIntegrationTests.cs	Adds a Taproot-focused Payjoin integration test asserting correct inclusion and shape of the receiver input.

🧠 Review effort: Lite

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[Copilot]

🟡 Changes recommended

The regression test still reaches the unfixed generic input constructor and fails before completing payment.

1 open finding

• Fix Taproot receiver input weight prediction in PayAsync · New

3 resolved since last review

• The weight calculation here is fragile and may be incorrect depending on what NBitcoin includes in…
• The PR title indicates a production fix (\"fix: Fix Taproot receiver input handling\"), but the…
• The positional boolean argument (..., true, ...) makes the test harder to read/maintain because…

🧠 Review effort: Balanced

[Copilot]

🟡 Changes recommended

The recorded rust-payjoin submodule lacks the newly called constructors, preventing clean CI builds.

1 open finding

• Update rust-payjoin submodule for typed constructor API · New

1 resolved since last review

• Fix Taproot receiver input weight prediction in PayAsync

🧠 Review effort: Balanced

[Copilot]

🟢 Approval recommended

The typed-constructor fix is consistent with the updated FFI API and has focused unit and end-to-end regression coverage.

0 open findings

1 resolved since last review

• Update rust-payjoin submodule for typed constructor API

🧠 Review effort: Balanced

[chavic]

cACK 23c7cd1