plugin: nwc: consider routing fees for payment budget

diff --git a/electrum/plugins/nwc/nwcserver.py b/electrum/plugins/nwc/nwcserver.py
index a050746..bd82509 100644
--- a/electrum/plugins/nwc/nwcserver.py
+++ b/electrum/plugins/nwc/nwcserver.py
@@ -42,7 +42,7 @@ from electrum.util import log_exceptions, ca_path, OldTaskGroup, get_asyncio_loo
     get_running_loop, run_sync_function_on_asyncio_thread
 from electrum.invoices import Invoice, Request, PR_UNKNOWN, PR_PAID, BaseInvoice, PR_INFLIGHT, PR_FAILED, PR_EXPIRED, PR_UNPAID
 from electrum import constants
-from electrum.lnutil import RECEIVED
+from electrum.lnutil import RECEIVED, PaymentFeeBudget
 
 if TYPE_CHECKING:
     from aiohttp_socks import ProxyConnector
@@ -780,7 +780,7 @@ class NWCServer(Logger, EventListener):
         payment_info = self.get_payment_info(key)
         if not payment_info:
             return
-        _, fee_msat, _, settled_at = payment_info
+        _, _, fee_msat, settled_at = payment_info
 
         assert key == invoice.rhash, f"{key=!r} != {invoice.rhash=!r}"
         notification = {
@@ -816,25 +816,43 @@ class NWCServer(Logger, EventListener):
         elif invoice.get_amount_msat() is None:
             invoice.set_amount_msat(amount_msat)
 
-        budget_item = self.add_to_budget(request_pub, msat_requested=amount_msat or invoice.get_amount_msat())
-        if not budget_item:
-            return self.get_error_response("QUOTA_EXCEEDED", "Payment exceeds daily limit")
+        # add the maximum allowed fee to the budget and update it with the actual fee once the payment succeeds
+        # to prevent exceeding the budget through high fees
+        payment_amount_msat = amount_msat or invoice.get_amount_msat()
+        fee_budget = PaymentFeeBudget.from_invoice_amount(
+            config=self.wallet.config,
+            invoice_amount_msat=payment_amount_msat,
+        )
+        budget_amount_msat = payment_amount_msat + fee_budget.fee_msat
+        try:
+            budget_item = self.add_to_budget(request_pub, msat_requested=budget_amount_msat)
+        except ValueError as e:
+            return self.get_error_response("QUOTA_EXCEEDED", str(e))
 
         self.wallet.save_invoice(invoice)
         success = None
         try:
             success, log = await self.wallet.lnworker.pay_invoice(
                 invoice=invoice,
-                amount_msat=amount_msat
+                amount_msat=amount_msat,
+                budget=fee_budget,
             )
         except Exception as e:
             self.logger.exception(f"failed to pay nwc invoice")
             return self.get_error_response("PAYMENT_FAILED", str(e))
         finally:
-            if success is False:
-                # If the user shuts down or the application crashes before the payment ends, it will not
-                # get deducted from the budget, even if the htlcs later get failed on wallet restart.
+            # note: if the user shuts down or the application crashes before the payment ends, it will not
+            # get deducted from the budget, even if the htlcs later get failed on wallet restart.
+            if success:
+                # replace the spend in the budget, this time using the actual (lower) fees that have been paid
+                info = self.get_payment_info(invoice.rhash)
+                assert info, "info should exist after successful payment"
+                _, total_amount_msat, _, _ = info
+                assert payment_amount_msat <= total_amount_msat <= budget_amount_msat
+                self._update_budget_item_amount(request_pub, old_budget_item=budget_item, new_msat=total_amount_msat)
+            else:
                 self.remove_from_budget(request_pub, budget_item)
+
         preimage: bytes = self.wallet.lnworker.get_preimage(bytes.fromhex(invoice.rhash))
         response = {}
         if not success or not preimage:
@@ -853,7 +871,9 @@ class NWCServer(Logger, EventListener):
         budget_spends = self.connections[client_pub].get('budget_spends', [])
         try:
             budget_spends.remove(budget_item)
+            self.logger.debug(f"removed {budget_item=} from {client_pub[:4]}...{client_pub[-4:]} budget")
         except ValueError:
+            self.logger.debug(f"failed to remove {budget_item=} from {client_pub[:4]}...{client_pub[-4:]} budget: not found")
             pass
 
     def get_used_budget_msat(self, client_pub: str) -> int:
@@ -876,7 +896,7 @@ class NWCServer(Logger, EventListener):
                     continue  # could happen if there is a race
         return used_budget
 
-    def add_to_budget(self, client_pub: str, *, msat_requested: int) -> Optional[list[int]]:
+    def add_to_budget(self, client_pub: str, *, msat_requested: int) -> list[int]:
         if 'budget_spends' not in self.connections[client_pub]:
             self.connections[client_pub]['budget_spends'] = []
 
@@ -885,13 +905,27 @@ class NWCServer(Logger, EventListener):
         if client_budget_sat is not None:
             used_budget_msat: int = self.get_used_budget_msat(client_pub)
             if used_budget_msat + msat_requested > client_budget_sat * 1000:
-                return None
+                raise ValueError("spend exceeds daily budget")
 
+        self.logger.debug(f"adding {msat_requested=} msat to {client_pub[:4]}...{client_pub[-4:]} budget")
         # tuples don't work because jsondb converts them to lists on reload
         budget_item = [msat_requested, int(time.time())]
         self.connections[client_pub]['budget_spends'].append(budget_item)
         return budget_item
 
+    def _update_budget_item_amount(self, client_pub: str, *, old_budget_item: list[int], new_msat: int) -> None:
+        assert len(old_budget_item) == 2, old_budget_item
+        budget_spends = self.connections[client_pub].setdefault('budget_spends', [])
+        try:
+            budget_spends.remove(old_budget_item)
+        except ValueError:
+            self.logger.debug(
+            f"failed to rm and update {old_budget_item=} from {client_pub[:4]}...{client_pub[-4:]} budget: not found")
+            return
+        # tuples don't work because jsondb converts them to lists on reload
+        new_budget_item = [new_msat, int(time.time())]
+        budget_spends.append(new_budget_item)
+
     async def publish_info_event(self):
         """
         Publishes the info event according to spec, announcing the supported methods.