Emit SpliceFailed event when splice initialization fails during quiescence

Users need to be notified when splice operations fail at any stage. Previously,
splice failures during the quiescence initialization phase were not reported,
leaving users unaware of failed splice attempts.

Now emits Event::SpliceFailed when send_splice_init fails during stfu processing
of QuiescentAction::Splice, ensuring consistent splice failure reporting across
all phases of the splice lifecycle.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jkczyz

lightning/src/ln/channel.rs

@@ -12832,27 +12832,27 @@ where
 	#[rustfmt::skip]
 	pub fn stfu<L: Deref>(
 		&mut self, msg: &msgs::Stfu, logger: &L
-	) -> Result<Option<StfuResponse>, ChannelError> where L::Target: Logger {
+	) -> Result<Option<StfuResponse>, (ChannelError, Option<SpliceFundingFailed>)> where L::Target: Logger {
 		if self.context.channel_state.is_quiescent() {
-			return Err(ChannelError::Warn("Channel is already quiescent".to_owned()));
+			return Err((ChannelError::Warn("Channel is already quiescent".to_owned()), None));
 		}
 		if self.context.channel_state.is_remote_stfu_sent() {
-			return Err(ChannelError::Warn(
+			return Err((ChannelError::Warn(
 				"Peer sent `stfu` when they already sent it and we've yet to become quiescent".to_owned()
-			));
+			), None));
 		}
 
 		if !self.context.is_live() {
-			return Err(ChannelError::Warn(
+			return Err((ChannelError::Warn(
 				"Peer sent `stfu` when we were not in a live state".to_owned()
-			));
+			), None));
 		}
 
 		if !self.context.channel_state.is_local_stfu_sent() {
 			if !msg.initiator {
-				return Err(ChannelError::WarnAndDisconnect(
+				return Err((ChannelError::WarnAndDisconnect(
 					"Peer sent unexpected `stfu` without signaling as initiator".to_owned()
-				));
+				), None));
 			}
 
 			// We don't check `is_waiting_on_peer_pending_channel_update` prior to setting the flag
@@ -12866,7 +12866,7 @@ where
 			return self
 				.send_stfu(logger)
 				.map(|stfu| Some(StfuResponse::Stfu(stfu)))
-				.map_err(|e| ChannelError::Ignore(e.to_owned()));
+				.map_err(|e| (ChannelError::Ignore(e.to_owned()), None));
 		}
 
 		// We already sent `stfu` and are now processing theirs. It may be in response to ours, or
@@ -12885,9 +12885,9 @@ where
 			// have a monitor update pending if we've processed a message from the counterparty, but
 			// we don't consider this when becoming quiescent since the states are not mutually
 			// exclusive.
-			return Err(ChannelError::WarnAndDisconnect(
+			return Err((ChannelError::WarnAndDisconnect(
 				"Received counterparty stfu while having pending counterparty updates".to_owned()
-			));
+			), None));
 		}
 
 		self.context.channel_state.clear_local_stfu_sent();
@@ -12903,14 +12903,25 @@ where
 			match self.quiescent_action.take() {
 				None => {
 					debug_assert!(false);
-					return Err(ChannelError::WarnAndDisconnect(
+					return Err((ChannelError::WarnAndDisconnect(
 						"Internal Error: Didn't have anything to do after reaching quiescence".to_owned()
-					));
+					), None));
 				},
 				Some(QuiescentAction::Splice(_instructions)) => {
 					return self.send_splice_init(_instructions)
 						.map(|splice_init| Some(StfuResponse::SpliceInit(splice_init)))
-						.map_err(|e| ChannelError::WarnAndDisconnect(e.to_owned()));
+						.map_err(|e| {
+							let splice_failed = SpliceFundingFailed {
+								channel_id: self.context.channel_id,
+								counterparty_node_id: self.context.counterparty_node_id,
+								user_channel_id: self.context.user_id,
+								funding_txo: None,
+								channel_type: None,
+								contributed_inputs: Vec::new(),
+								contributed_outputs: Vec::new(),
+							};
+							(ChannelError::WarnAndDisconnect(e.to_owned()), Some(splice_failed))
+						});
 				},
 				#[cfg(any(test, fuzzing))]
 				Some(QuiescentAction::DoNothing) => {

lightning/src/ln/channelmanager.rs

@@ -11033,7 +11033,25 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 					);
 
 					let res = chan.stfu(&msg, &&logger);
-					let resp = try_channel_entry!(self, peer_state, res, chan_entry);
+					let resp = match res {
+						Ok(resp) => resp,
+						Err((e, splice_funding_failed)) => {
+							// Emit SpliceFailed event if there was an active splice negotiation
+							if let Some(splice_failed) = splice_funding_failed {
+								let pending_events = &mut self.pending_events.lock().unwrap();
+								pending_events.push_back((events::Event::SpliceFailed {
+									channel_id: splice_failed.channel_id,
+									counterparty_node_id: splice_failed.counterparty_node_id,
+									user_channel_id: splice_failed.user_channel_id,
+									funding_txo: splice_failed.funding_txo,
+									channel_type: splice_failed.channel_type,
+									contributed_inputs: splice_failed.contributed_inputs,
+									contributed_outputs: splice_failed.contributed_outputs,
+								}, None));
+							}
+							try_channel_entry!(self, peer_state, Err(e), chan_entry)
+						},
+					};
 					match resp {
 						None => Ok(false),
 						Some(StfuResponse::Stfu(msg)) => {