fix(psbt): route addOutput unknownKeyVals to output map - #21
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addOutput() was calling addUnknownKeyValToInput(outputIndex, keyVal)
instead of addUnknownKeyValToOutput(outputIndex, keyVal). This caused
two confirmed failure modes:
1. Silent corruption when outputIndex < inputs.length: the keyval was
attached to inputs[outputIndex].unknownKeyVals and survived
serialize/parse round-trips in the wrong (input) map. Because the
duplicate-check also ran against InputTypes (16 entries) instead of
OutputTypes (6 entries), output unknown-key type bytes 6–15 were
additionally misrejected.
2. Crash ("No input #N") when outputIndex >= inputs.length — the
common 1-input/2-output case — making PSBT construction impossible
whenever unknownKeyVals accompany the second output.
Both modes affect musig2/MPC coordination data carried as output
proprietary fields: the signing ceremony crashes or corrupts the PSBT,
leaving funds stuck in the shared wallet.
Fix: change line 159 to call addUnknownKeyValToOutput, matching the
upstream bip174 v2.1.1 fix. Add regression tests covering correct
placement, round-trip survival, and the outputs>inputs case.
Ticket: WCN-1934
Session-Id: 9abd2e08-b701-4f8d-9355-06124e17bf0c
Task-Id: edef13cc-a93b-4c12-85ac-d51bcc1dfaaa
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What
`this.addUnknownKeyValToInput(outputIndex, keyVal)` →
`this.addUnknownKeyValToOutput(outputIndex, keyVal)`.
(not `inputs[N].unknownKeyVals`) and survive a `toHex()`/`fromHex()` round-trip.
of outputs exceeds the number of inputs (e.g. 1-input / 2-output transactions).
Why
`addOutput()` was calling the input variant of `addUnknownKeyVal` instead of
the output variant, causing two confirmed failure modes (WCN-1934 / FND-001):
Silent corruption when `outputIndex < inputs.length`: the keyval was
attached to `inputs[outputIndex].unknownKeyVals` and survived
serialize/parse round-trips in the wrong map. The PSBT proprietary-key
support added for musig2/MPC coordination data (commit 8a33996) was
completely broken: co-signers never found the required output metadata,
causing signing ceremonies to fail with funds stuck.
Crash (`"No input #N"`) when `outputIndex >= inputs.length` — the
common 1-input / 2-output case — making PSBT construction impossible
whenever `unknownKeyVals` accompany outputs beyond the first.
Additionally, the old code ran the duplicate/type guard against `InputTypes`
(16 entries) instead of `OutputTypes` (6 entries), so output unknown keys with
type byte 6–15 were additionally misrejected. This is addressed in pt2.
Test plan
Stack
This PR is part 1 of 2 in a stack. Review and merge in order:
Ticket: WCN-1934