lnwatcher: keep_watching should wait at least until closing_tx is deep

Even if it decides there is nothing to sweep from the ctx/etc, it still needs to
keep watching until a reorg-safe depth.

Author: SomberNight

electrum/lnwatcher.py

@@ -99,6 +99,7 @@ async def check_onchain_situation(self, address: str, funding_outpoint: str) ->
         if not self.adb.is_mine(address):
             return
         # inspect_tx_candidate might have added new addresses, in which case we return early
+        # note: maybe we should wait until adb.is_up_to_date... (?)
         funding_txid = funding_outpoint.split(':')[0]
         funding_height = self.adb.get_tx_height(funding_txid)
         closing_txid = self.adb.get_spender(funding_outpoint)
@@ -159,7 +160,9 @@ async def sweep_commitment_transaction(self, funding_outpoint: str, closing_tx:
             return False
         # detect who closed and get information about how to claim outputs
         is_local_ctx, sweep_info_dict = chan.get_ctx_sweep_info(closing_tx)
-        keep_watching = False if sweep_info_dict else not self.adb.is_deeply_mined(closing_tx.txid())
+        # note: we need to keep watching *at least* until the closing tx is deeply mined,
+        #       possibly longer if there are TXOs to sweep
+        keep_watching = not self.adb.is_deeply_mined(closing_tx.txid())
         # create and broadcast transactions
         for prevout, sweep_info in sweep_info_dict.items():
             prev_txid, prev_index = prevout.split(':')
@@ -170,7 +173,7 @@ async def sweep_commitment_transaction(self, funding_outpoint: str, closing_tx:
                 self.logger.info(f'prevout does not exist for {name}: {prevout}')
                 continue
             was_added = self.maybe_redeem(sweep_info)
-            spender_txid = self.adb.get_spender(prevout)
+            spender_txid = self.adb.get_spender(prevout)  # note: LOCAL spenders don't count
             spender_tx = self.adb.get_transaction(spender_txid) if spender_txid else None
             if spender_tx:
                 # the spender might be the remote, revoked or not

electrum/plugins/watchtower/watchtower.py

@@ -202,9 +202,10 @@ def inspect_tx_candidate(self, outpoint, n: int) -> Dict[str, str]:
                 result.update(r)
         return result
 
-    async def sweep_commitment_transaction(self, funding_outpoint, closing_tx):
+    async def sweep_commitment_transaction(self, funding_outpoint: str, closing_tx: Transaction) -> bool:
+        assert closing_tx
         spenders = self.inspect_tx_candidate(funding_outpoint, 0)
-        keep_watching = False
+        keep_watching = not self.adb.is_deeply_mined(closing_tx.txid())
         for prevout, spender in spenders.items():
             if spender is not None:
                 keep_watching |= not self.adb.is_deeply_mined(spender)