Fix floating point rounding in wallet balance properties (#2583)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/cryptoadvance/specter/wallet/wallet.py

@@ -1473,7 +1473,7 @@ class Wallet(AbstractWallet):
         for utxo in self.locked_utxo:
             if utxo["txid"] in frozen_txid:
                 amount += utxo["amount"]
-        return amount
+        return round(amount, 8)
 
     @property
     def amount_locked_unsigned(self):
@@ -1481,7 +1481,7 @@ class Wallet(AbstractWallet):
         amount = 0
         for psbt in self.pending_psbts.values():
             amount += sum([inp.float_amount for inp in psbt.inputs])
-        return amount
+        return round(amount, 8)
 
     @property
     def amount_immature(self):
@@ -1496,7 +1496,9 @@ class Wallet(AbstractWallet):
     @property
     def amount_available(self):
         """All outputs minus UTXO locked in unsigned transactions and frozen outputs"""
-        return self.amount_total - self.amount_locked_unsigned - self.amount_frozen
+        return round(
+            self.amount_total - self.amount_locked_unsigned - self.amount_frozen, 8
+        )
 
     @property
     def fullbalance(self):

tests/test_wallet.py

@@ -367,3 +367,65 @@ def test_multiple_outputs_in_one_tx(
     assert full_utxo[1]["amount"] == 2
     assert full_utxo[2]["amount"] == 3
     assert full_utxo[3]["amount"] == 20
+
+
+@pytest.mark.slow
+def test_amount_available_floating_point_precision(
+    bitcoin_regtest, unfunded_hot_wallet_1: Wallet
+):
+    """Regression: balance properties must round to satoshi precision.
+
+    Without rounding, IEEE 754 float subtraction can produce values like
+    0.09055627999... instead of 0.09055628, causing false "insufficient
+    funds" errors when sending exactly the available balance.
+    """
+    wallet = unfunded_hot_wallet_1
+    amounts = [0.09055628, 0.09317884, 0.14306287]
+
+    # Sanity: these amounts trigger IEEE 754 drift when subtracted
+    assert sum(amounts) - amounts[1] - amounts[2] != amounts[0]
+
+    for amt in amounts:
+        bitcoin_regtest.testcoin_faucet(wallet.getnewaddress(), amount=amt)
+    wallet.update()
+
+    assert wallet.amount_total == round(sum(amounts), 8)
+
+    # Freeze 2 UTXOs — their amounts will be subtracted from available
+    unspents = wallet.rpc.listunspent()
+    assert len(unspents) == 3
+    utxos_to_freeze = [
+        u for u in unspents if u["amount"] in (amounts[1], amounts[2])
+    ]
+    wallet.toggle_freeze_utxo(
+        [f"{u['txid']}:{u['vout']}" for u in utxos_to_freeze]
+    )
+    wallet.check_utxo()
+
+    assert wallet.amount_frozen == round(amounts[1] + amounts[2], 8)
+    assert wallet.amount_available == amounts[0]
+
+    # Create a PSBT locking 2 UTXOs instead of freezing
+    wallet.toggle_freeze_utxo(
+        [f"{u['txid']}:{u['vout']}" for u in utxos_to_freeze]
+    )
+    wallet.check_utxo()
+    assert wallet.amount_frozen == 0.0
+
+    selected_coins = [
+        {"txid": u["txid"], "vout": u["vout"]} for u in utxos_to_freeze
+    ]
+    random_address = "bcrt1q7mlxxdna2e2ufzgalgp5zhtnndl7qddlxjy5eg"
+    psbt = wallet.createpsbt(
+        [random_address],
+        [round(amounts[1] + amounts[2], 8)],
+        True,
+        0,
+        1,
+        selected_coins=selected_coins,
+    )
+
+    assert wallet.amount_locked_unsigned == round(amounts[1] + amounts[2], 8)
+    assert wallet.amount_available == amounts[0]
+
+    wallet.delete_pending_psbt(psbt.to_dict()["tx"]["txid"])