qml: show warning in ConfirmTxDialog if max amount cannot be fully sent due to channel reserve requirements.

electrum/gui/qml/components/controls/TxOutput.qml

@@ -14,7 +14,9 @@ TextHighlightPane {
     property int idx: -1
 
     property string _suffix: model.is_mine || model.is_change
-            ? qsTr('mine')
+            ? model.is_reserve
+                ? qsTr('reserve')
+                : qsTr('mine')
             : model.is_swap
                 ? qsTr('swap')
                 : model.is_billing

electrum/gui/qml/qetxfinalizer.py

@@ -275,7 +275,8 @@ class TxFeeSlider(FeeSlider):
                 'is_mine': self._wallet.wallet.is_mine(o.get_ui_address_str()),
                 'is_change': self._wallet.wallet.is_change(o.get_ui_address_str()),
                 'is_billing': self._wallet.wallet.is_billing_address(o.get_ui_address_str()),
-                'is_swap': False if not sm else sm.is_lockup_address_for_a_swap(o.get_ui_address_str()) or o.get_ui_address_str() == DummyAddress.SWAP
+                'is_swap': False if not sm else sm.is_lockup_address_for_a_swap(o.get_ui_address_str()) or o.get_ui_address_str() == DummyAddress.SWAP,
+                'is_reserve': o.is_utxo_reserve
             })
         self.outputs = outputs
 
@@ -417,6 +418,15 @@ class QETxFinalizer(TxFeeSlider):
 
         self.update_fee_warning_from_tx(tx=tx, invoice_amt=amount)
 
+        if self._amount.isMax and not self.warning:
+            if reserve_sats := sum(txo.value for txo in tx.outputs() if txo.is_utxo_reserve):
+                reserve_str = self._config.format_amount_and_units(reserve_sats)
+                self.warning = ' '.join([
+                    _('Warning') + ':',
+                    _('Could not spend max: a security reserve of {} was kept for your Lightning channels.')
+                    .format(reserve_str)
+                ])
+
         self._valid = True
         self.validChanged.emit()