Minimize gift lock-up: best-fit coins + optional pre-split

Gift coin selection now picks the smallest single coin that covers the gift
(was largest-first), locking the least value until claim. When no near-exact
coin exists, offer to pre-split: broadcast a self-send carving out a gift+dust
coin so the gift later locks only ~the gift amount.

The split is only offered when the liquidity it frees (lock - gift - dust)
exceeds the split's own fee, so it never costs more than it regains. Decision
is surfaced as an interstitial on Create, since a full re-render drops input
focus and a live preview isn't viable.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 60 insertions, 2 deletions

diff --git a/src/app.js b/src/app.js
index ae21240..cae97d0 100644
--- a/src/app.js
+++ b/src/app.js
@@ -49,6 +49,8 @@ const ui = {
   giftAmount: '', // gift-create amount input
   giftCode: null, // last-created gift PSBT code
   giftError: '',
+  giftSplitOffer: null, // { amt, lock, freed, fee } when offering to split a coin first
+  giftSplitTxid: null, // txid of a broadcast pre-split, awaiting confirmation
   revokeId: null, // outpoint of a gift being revoked (confirm state)
   claimCode: null, // gift code being claimed (opened from a #gift= link)
   claimedAmount: 0,
@@ -872,6 +874,8 @@ function lock() {
   ui.giftAmount = '';
   ui.giftCode = null;
   ui.giftError = '';
+  ui.giftSplitOffer = null;
+  ui.giftSplitTxid = null;
   ui.revokeId = null;
   ui.receiveSeenIndex = null;
   ui.txDetail = null;
@@ -1005,12 +1009,48 @@ function createGiftLink() {
   const min = giftMinimum(rate);
   const amt = parseAmount(ui.giftAmount, unit); // entered in the current display unit
   if (!amt || amt < min) { ui.giftError = t('giftAmountInvalid', { n: fmtAmount(min) + ' ' + unitLabel() }); render(); return; }
+  // Creating the gift now locks the whole source coin until it's claimed. If
+  // best-fit can't find a near-exact coin, a pre-split would shrink the locked
+  // change down to a dust pad (294) — worth offering only when the liquidity it
+  // frees exceeds the split's own fee (otherwise you'd pay more than you regain).
+  const lock = wallet.giftLockPreview(amt);
+  const splitFee = Math.ceil((11 + 68 + 31 * 2) * Math.max(1, Math.round(rate)));
+  const freed = lock != null ? lock - amt - 294 : 0;
+  if (lock != null && freed > splitFee && !wallet.offline) {
+    ui.giftSplitOffer = { amt, lock, freed, fee: splitFee };
+    ui.giftError = '';
+    render();
+    return;
+  }
+  doCreateGift(amt, rate);
+}
+function doCreateGift(amt, rate) {
   try {
     ui.giftCode = wallet.createGift(amt, rate).code;
     ui.giftError = '';
+    ui.giftSplitOffer = null;
+    ui.giftSplitTxid = null;
   } catch (e) {
     ui.giftError = e.message;
+    ui.giftSplitOffer = null;
+  }
+  render();
+}
+// Pre-split: broadcast a self-send that carves out a right-sized coin so the
+// later gift locks only ~the gift amount. The gift can be created once it
+// confirms (best-fit then picks the carve-out automatically).
+async function doSplitForGift(amt) {
+  if (wallet.offline) { ui.giftError = t('scanOffline'); render(); return; }
+  ui.busy = true; ui.giftError = ''; render();
+  try {
+    const rate = (wallet.feeRates && wallet.feeRates.halfHourFee) || 5;
+    ui.giftSplitTxid = await wallet.splitForGift(amt, rate);
+    ui.giftSplitOffer = null;
+    wallet.scan().catch(() => {});
+  } catch (e) {
+    ui.giftError = e.message || t('giftSplitFailed');
   }
+  ui.busy = false;
   render();
 }
 function giftCard() {
@@ -1027,9 +1067,26 @@ function giftCard() {
           h('div', { class: 'addr-box break', style: 'width:100%;font-size:12px' }, giftUrl()),
           h('div', { class: 'row gap6 wrap' },
             copyBtn(giftUrl(), t('copyLink')),
-            h('button', { class: 'btn-sm grow', onClick: () => { ui.giftCode = null; ui.giftAmount = ''; render(); } }, t('giftAnother'))
+            h('button', { class: 'btn-sm grow', onClick: () => { ui.giftCode = null; ui.giftAmount = ''; ui.giftSplitTxid = null; render(); } }, t('giftAnother'))
           )
         )
+      : ui.giftSplitOffer
+      ? (() => {
+          const o = ui.giftSplitOffer;
+          const u = ' ' + unitLabel();
+          return h('div', { class: 'col gap6' },
+            h('div', { class: 'small muted' },
+              t('giftSplitExplain', { lock: fmtAmount(o.lock) + u, change: fmtAmount(o.lock - o.amt) + u, fee: fmtAmount(o.fee) + u })),
+            ui.giftError && h('div', { class: 'notice err' }, ui.giftError),
+            ui.busy
+              ? h('button', { class: 'btn-primary btn-block', disabled: true }, h('span', { class: 'spinner' }))
+              : h('div', { class: 'col gap6' },
+                  h('button', { class: 'btn-primary btn-block', onClick: () => doSplitForGift(o.amt) }, t('giftSplitFirst')),
+                  h('button', { class: 'btn-block', onClick: () => doCreateGift(o.amt, giftRate()) }, t('giftLockWhole', { n: fmtAmount(o.lock) + u })),
+                  h('button', { class: 'linklike small', style: 'align-self:center', onClick: () => { ui.giftSplitOffer = null; render(); } }, t('back'))
+                )
+          );
+        })()
       : h('div', { class: 'col gap6' },
           h('div', { class: 'input-group' },
             h('input', { type: 'number', step: unit === 'sats' ? '1' : '0.00000001', min: '0', inputmode: 'decimal', placeholder: t('giftAmountLabel'),
@@ -1037,6 +1094,7 @@ function giftCard() {
             h('div', { style: 'display:flex;align-items:center' }, unitTag())
           ),
           h('div', { class: 'small faint' }, t('giftMinNote', { n: fmtAmount(giftMinimum(giftRate())) + ' ' + unitLabel() })),
+          ui.giftSplitTxid ? h('div', { class: 'notice ok' }, t('giftSplitPending')) : null,
           ui.giftError && h('div', { class: 'notice err' }, ui.giftError),
           h('button', { class: 'btn-block', onClick: createGiftLink }, t('giftLinkReveal'))
         ),
@@ -1567,7 +1625,7 @@ function giftView() {
     'div',
     { class: 'col', style: 'gap:12px' },
     giftCard(),
-    h('button', { class: 'btn-ghost btn-block', onClick: () => { ui.giftMode = false; ui.giftCode = null; ui.giftError = ''; ui.revokeId = null; render(); } }, t('back'))
+    h('button', { class: 'btn-ghost btn-block', onClick: () => { ui.giftMode = false; ui.giftCode = null; ui.giftError = ''; ui.giftSplitOffer = null; ui.giftSplitTxid = null; ui.revokeId = null; render(); } }, t('back'))
   );
 }