fix: Construct closing TX based on original funding TXO

lightning/src/ln/channel.rs

@@ -1778,7 +1778,10 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		assert!(self.shutdown_scriptpubkey.is_some());
 		let holder_shutdown_script = self.get_closing_scriptpubkey();
 		let counterparty_shutdown_script = self.counterparty_shutdown_scriptpubkey.clone().unwrap();
-		let funding_outpoint = self.funding_outpoint().into_bitcoin_outpoint();
+
+		// The closing transaction should always spend from the _original_ funding outpoint
+		// (NOT the `glue_transaction`).
+		let funding_outpoint = self.original_funding_outpoint().into_bitcoin_outpoint();
 
 		let closing_transaction = ClosingTransaction::new(value_to_holder as u64, value_to_counterparty as u64, holder_shutdown_script, counterparty_shutdown_script, funding_outpoint);
 		(closing_transaction, total_fee_satoshis)
@@ -1788,6 +1791,13 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		self.channel_transaction_parameters.funding_outpoint.unwrap()
 	}
 
+	fn original_funding_outpoint(&self) -> OutPoint {
+		match self.channel_transaction_parameters.original_funding_outpoint {
+			Some(outpoint) => outpoint,
+			None => self.funding_outpoint(),
+		}
+	}
+
 	#[inline]
 	/// Creates a set of keys for build_commitment_transaction to generate a transaction which our
 	/// counterparty will sign (ie DO NOT send signatures over a transaction created by this to