XRebalancePartMonitor: parse first_hop/return_hop as scidds

Found live via a probe subscriber: the plugin reports first_hop and
return_hop as SCIDDs ("305293x6x2/1"), but the monitor fed them to
Ln::Scid, which throws BacktraceException<std::invalid_argument> --
and the handler's catch(std::runtime_error) does not cover
logic_error, so every completed part died silently between the amount
parse and the attribution: no Error line, no Warn, no accounting.
The unit test's hand-written payloads used plain scids and kept
passing.

Strip the direction suffix before the Ln::Scid parse (the mapper keys
on the channel alone), widen the catch to std::exception so a future
payload surprise logs instead of vanishing, and reshape the test
payloads to the live-captured form, direction suffixes included.

Boss/Mod/XRebalancePartMonitor.cpp

@@ -36,6 +36,14 @@ void XRebalancePartMonitor::start() {
 		auto return_scid = Ln::Scid();
 		auto amount = Ln::Amount();
 		auto fee = Ln::Amount();
+		/* first_hop / return_hop are scidds ("845x1x0/1"); the
+		 * mapper keys on the channel alone, so drop the
+		 * direction suffix.  */
+		auto scid_of_scidd = [](std::string const& s) {
+			auto slash = s.find('/');
+			return Ln::Scid( slash == std::string::npos
+				       ? s : s.substr(0, slash));
+		};
 		try {
 			/* Custom notifications arrive with the sender's
 			 * payload AS params (lightningd relays it verbatim,
@@ -55,10 +63,10 @@ void XRebalancePartMonitor::start() {
 			if (std::string(payload["status"]) != "complete")
 				return Ev::lift();
 
-			first_scid = Ln::Scid(std::string(
+			first_scid = scid_of_scidd(std::string(
 				payload["first_hop"]
 			));
-			return_scid = Ln::Scid(std::string(
+			return_scid = scid_of_scidd(std::string(
 				payload["return_hop"]
 			));
 			amount = Ln::Amount::object(
@@ -67,7 +75,11 @@ void XRebalancePartMonitor::start() {
 			fee = Ln::Amount::object(
 				payload["fee_msat"]
 			);
-		} catch (std::runtime_error const& err) {
+		/* std::exception, not std::runtime_error: Ln::Scid
+		 * throws invalid_argument (a logic_error), and a
+		 * narrower catch let exactly that escape unlogged --
+		 * the silent-attribution-loss bug.  */
+		} catch (std::exception const& err) {
 			return Boss::log( bus, Error
 					, "XRebalancePartMonitor: unexpected "
 					  "xrebalance_part payload: %s: %s"

tests/boss/test_xrebalancepartmonitor.cpp

@@ -39,18 +39,20 @@ auto const listpeers_result = R"JSON(
 }
 )JSON";
 
-/* The plugin's Part::json shape: plain-number msat fields, real scids
- * on first_hop / return_hop, label appended by the notifier.  Custom
- * notifications deliver this AS params (lightningd relays the sender's
- * payload verbatim; no topic-key nesting, that is a built-in-topic
- * convention).  */
+/* The plugin's Part::json shape, as captured live off a probe
+ * subscriber (2026-07-23, lab0-a): plain-number msat fields, real
+ * SCIDDs (direction-suffixed) on first_hop / return_hop, label
+ * appended by the notifier.  Custom notifications deliver this AS
+ * params (lightningd relays the sender's payload verbatim; cln-plugin
+ * 0.7.0 also nests a copy under the topic key, which consumers should
+ * ignore).  */
 auto const complete_part = R"JSON(
 {
   "part_index": 2,
   "payment_hash": "f5a6a059a25d1e329d9b094aeeec8c2191ca037d3f5b0662e21ae850debe8ea2",
   "status": "complete",
-  "first_hop": "1000x1x1",
-  "return_hop": "1000x1x0",
+  "first_hop": "1000x1x1/1",
+  "return_hop": "1000x1x0/0",
   "planned_msat": 10000000,
   "delivered_msat": 10000000,
   "sent_msat": 10005958,
@@ -68,8 +70,8 @@ auto const failed_part = R"JSON(
   "part_index": 1,
   "payment_hash": "9d9b094aeeec8c2191ca037d3f5b0662e21ae850debe8ea2f5a6a059a25d1e32",
   "status": "failed",
-  "first_hop": "1000x1x1",
-  "return_hop": "1000x1x0",
+  "first_hop": "1000x1x1/1",
+  "return_hop": "1000x1x0/0",
   "planned_msat": 10000000,
   "delivered_msat": 0,
   "sent_msat": 10005958,