fix(lightning): actionable expired-invoice error + payment failures reach the user

- payments.rs: an expired invoice can never succeed on retry, so the
  error now says so and tells the payer the way out (ask the recipient
  for a fresh invoice) instead of echoing LND's raw reason.
- middleware.rs: the error sanitizer masked every Lightning payment
  failure as 'Operation failed. Check server logs' — but LND's reasons
  ('invoice expired', 'unable to find a path') are written for the
  payer and are all actionable. 'Payment failed', 'Invalid payment
  request' and 'Missing payment_request' now pass through, with a
  regression test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/lnd/payments.rs

@@ -62,6 +62,14 @@ impl RpcHandler {
                 .get("message")
                 .and_then(|v| v.as_str())
                 .unwrap_or("Unknown error");
+            // Invoices are short-lived; retrying the same one can never
+            // succeed, so tell the user the way out instead of just the fact.
+            if msg.contains("invoice expired") {
+                return Err(anyhow::anyhow!(
+                    "Payment failed: this invoice has expired ({}). Ask the recipient for a fresh invoice and try again.",
+                    msg.trim_start_matches("invoice expired. ")
+                ));
+            }
             return Err(anyhow::anyhow!("Payment failed: {}", msg));
         }
 

core/archipelago/src/api/rpc/middleware.rs

@@ -79,6 +79,13 @@ pub(super) fn sanitize_error_message(msg: &str) -> String {
         // them in the first place (ecash send, 2026-07-22).
         "Insufficient balance",
         "Insufficient funds",
+        // Lightning payment failures carry LND's reason ("invoice expired.
+        // Valid until …", "no route", …) — the user can act on every one of
+        // them, and masking sent the operator to journalctl (invoice-expired
+        // send, 2026-07-23).
+        "Payment failed",
+        "Invalid payment request",
+        "Missing 'payment_request'",
         "Your Lightning node is still finishing",
         "Bitcoin address",
         "No router",
@@ -158,6 +165,25 @@ mod sanitize_tests {
         }
     }
 
+    #[test]
+    fn lightning_payment_errors_pass_through() {
+        // LND's payment-failure reasons are written for the payer — masking
+        // "invoice expired" as "Check server logs" left a user retrying a
+        // dead invoice (framework-pt, 2026-07-23).
+        for msg in [
+            "Payment failed: this invoice has expired (Valid until 2026-07-23 07:41:42 +0000 UTC). Ask the recipient for a fresh invoice and try again.",
+            "Payment failed: unable to find a path to destination",
+            "Invalid payment request: must be a Lightning invoice (lnbc...)",
+            "Missing 'payment_request' parameter",
+        ] {
+            assert_ne!(
+                sanitize_error_message(msg),
+                "Operation failed. Check server logs for details.",
+                "masked: {msg}"
+            );
+        }
+    }
+
     #[test]
     fn internal_errors_stay_generic() {
         assert_eq!(