Fix "Cannot mix BigInt and other types" when creating an on-chain gift.

_buildGiftPsbt (the v2 ephemeral-key gift builder) subtracted the funding fee — _giftFundFee returns a Number — directly from BigInt coin sums (sum - _giftFundFee(...), sum - gift - _giftFundFee(...)), which throws in JS. Any on-chain (Savings) gift creation hit it: "Split a coin first", "Lock the whole coin", and gift-all. Wrap the fee in BigInt at those sites (new fundFee() helper).

Adds tools/gift-build-test.js — the on-chain gift BUILDER had no coverage, which is how this shipped. It builds a specific-amount gift, a whole-balance gift, and the split carve-out shape (all three fee branches) against a mock wallet and asserts they produce claimable v2 codes without throwing.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01MGzU12QrAA4G6BYGzGVdXz

1 files changed, 4 insertions, 3 deletions

diff --git a/src/features/gifts-wallet.js b/src/features/gifts-wallet.js
index 920cddc..6776788 100644
--- a/src/features/gifts-wallet.js
+++ b/src/features/gifts-wallet.js
@@ -313,16 +313,17 @@ export function installGiftWallet(wallet) {
       const rate = Math.max(1, Math.round(feeRate || (this.feeRates && this.feeRates.halfHourFee) || 5));
       const sum = sel.reduce((s, u) => s + BigInt(u.value), 0n);
       const whole = gift >= sum; // createGiftAll: gift the entire selection
+      const fundFee = (nOut) => BigInt(_giftFundFee(sel.length, nOut, rate));
       let eAmount, change;
       if (whole) {
-        eAmount = sum - _giftFundFee(sel.length, 1, rate);
+        eAmount = sum - fundFee(1);
         change = 0n;
       } else {
-        change = sum - gift - _giftFundFee(sel.length, 2, rate);
+        change = sum - gift - fundFee(2);
         if (change >= DUST) { eAmount = gift; }
         // change would be dust: drop it into the fee, single output, honour the
         // requested amount (fee = sum - gift, which must clear a 1-output fee).
-        else { eAmount = gift; change = 0n; if (sum - gift < _giftFundFee(sel.length, 1, rate)) throw new Error('Not enough to cover the funding fee — try a smaller gift.'); }
+        else { eAmount = gift; change = 0n; if (sum - gift < fundFee(1)) throw new Error('Not enough to cover the funding fee — try a smaller gift.'); }
       }
       if (eAmount < DUST) throw new Error('Gift amount is too small.');
       // the throwaway key that holds the gift until the claimer sweeps it