1 files changed, 56 insertions, 33 deletions
diff --git a/src/features/ark.js b/src/features/ark.js
index b155d17..eccc3b8 100644
--- a/src/features/ark.js
+++ b/src/features/ark.js
@@ -2224,23 +2224,8 @@ export function arkFeature(ctx) {
       const spk = btc.OutScript.encode(btc.Address(wallet.netCfg.net).decode(target.address));
       // Offboarding moves whole vtxos, so carve out the exact amount first
       // when we're not sending everything.
-      const spendables = () => freeCoins(mgr.state);
-      const total = spendables().reduce((n, v) => n + v.amountSat, 0);
-      let ids;
-      if (amountSat < total) {
-        let exact = spendables().find((v) => v.amountSat === amountSat);
-        if (!exact) {
-          const before = new Set(spendables().map((v) => v.id));
-          await mgr.send(mgr.address(), amountSat);
-          for (let i = 0; i < 30 && !exact; i++) {
-            await new Promise((r) => setTimeout(r, 2000));
-            await mgr.sync().catch(() => {});
-            exact = spendables().find((v) => v.amountSat === amountSat && !before.has(v.id));
-          }
-          if (!exact) throw new Error(t('arkSplitTimeout'));
-        }
-        ids = [exact.id];
-      }
+      const total = freeCoins(mgr.state).reduce((n, v) => n + v.amountSat, 0);
+      const ids = amountSat < total ? await carveCoins(mgr, amountSat) : undefined;
       await mgr.startOffboard(spk, target.address, ids);
       return;
     }
@@ -3316,6 +3301,58 @@ export function arkFeature(ctx) {
       })());
   }
 
+  // A set of coins adding up to exactly `amountSat`: one coin of that size,
+  // else the smallest subset of the free coins that sums to it (largest coins
+  // first, so an offboard takes as few inputs as it can). null when no subset
+  // fits. Reachable sums are built up coin by coin, capped so a balance in
+  // hundreds of dust coins can't stall the tap.
+  function exactCoins(coins, amountSat) {
+    const one = coins.find((v) => v.amountSat === amountSat);
+    if (one) return [one];
+    const sorted = [...coins].filter((v) => v.amountSat > 0 && v.amountSat < amountSat).sort((a, b) => b.amountSat - a.amountSat);
+    const reach = new Map([[0, null]]); // sum -> { coin, prev } that first reached it
+    for (const v of sorted) {
+      const add = [];
+      for (const sum of reach.keys()) {
+        const next = sum + v.amountSat;
+        if (next <= amountSat && !reach.has(next)) add.push([next, { coin: v, prev: sum }]);
+      }
+      for (const [sum, via] of add) reach.set(sum, via);
+      if (reach.has(amountSat)) break;
+      if (reach.size > 50_000) return null;
+    }
+    if (!reach.has(amountSat)) return null;
+    const picked = [];
+    for (let sum = amountSat; sum > 0;) { const via = reach.get(sum); picked.push(via.coin); sum = via.prev; }
+    return picked;
+  }
+  // The coins that leave Spending for an on-chain send of `amountSat`. An
+  // offboard moves whole vtxos, so the amount has to be covered exactly:
+  // by coins already in the wallet when they fit (a balance that happens to
+  // add up, or the halves an earlier split left behind), else an exact amount
+  // is split off by paying it to this wallet's own address. A payment spread
+  // over several inputs arrives as several coins, one per input with the last
+  // carrying the remainder, so what the split yields is every coin that lands
+  // on the receive key and adds up to the amount, not a single coin of that
+  // size: looking for one made every partial on-chain send from a balance
+  // in two or more coins time out (Jarryd, 2026-10-23, three splits and no
+  // send). Change from the split carries its own key index and stays.
+  async function carveCoins(mgr, amountSat) {
+    const free = () => freeCoins(mgr.state);
+    const have = exactCoins(free(), amountSat);
+    if (have) return have.map((v) => v.id);
+    const before = new Set(free().map((v) => v.id));
+    await mgr.send(mgr.address(), amountSat);
+    for (let i = 0; i < 30; i++) {
+      await mgr.sync().catch(() => {});
+      const landed = free().filter((v) => !before.has(v.id) && !v.keyIndex);
+      const hit = exactCoins(landed, amountSat);
+      if (hit) return hit.map((v) => v.id);
+      await new Promise((r) => setTimeout(r, 2000));
+    }
+    throw new Error(t('arkSplitTimeout'));
+  }
+
   // vtxoIds: exactly these coins go (the coins page's ticked subset);
   // otherwise an amount is split off the balance, or everything goes.
   async function doArkOffboard(amountSat, destAddress = null, vtxoIds = undefined) {
@@ -3324,23 +3361,9 @@ export function arkFeature(ctx) {
       const address = destAddress || wallet.freshReceive().address;
       const spk = addrScript(address);
       const mgr = await connectArk();
-      const spendables = () => freeCoins(mgr.state);
-      const total = spendables().reduce((n, v) => n + v.amountSat, 0);
+      const total = freeCoins(mgr.state).reduce((n, v) => n + v.amountSat, 0);
       let ids = vtxoIds; // undefined = all spendable vtxos
-      if (!ids && amountSat && amountSat < total) {
-        let target = spendables().find((v) => v.amountSat === amountSat);
-        if (!target) {
-          const before = new Set(spendables().map((v) => v.id));
-          await mgr.send(mgr.address(), amountSat);
-          for (let i = 0; i < 30 && !target; i++) {
-            await new Promise((r) => setTimeout(r, 2000));
-            await mgr.sync().catch(() => {});
-            target = spendables().find((v) => v.amountSat === amountSat && !before.has(v.id));
-          }
-          if (!target) throw new Error(t('arkSplitTimeout'));
-        }
-        ids = [target.id];
-      }
+      if (!ids && amountSat && amountSat < total) ids = await carveCoins(mgr, amountSat);
       const action = await mgr.startOffboard(spk, address, ids);
       ui.arkOffboardAmt = '';
       ui.arkMoveOpen = false;