payment retries on simulated network

README.md

@@ -425,6 +425,8 @@ Included:
   count and value limitations set on channel creation.
 * Liquidity checks: HTLCs are only forwarded if the node has sufficient
   liquidity in the mocked channel.
+* Retries: a failed payment is re-routed up to 5 times, avoiding the
+  channels that rejected it, before it is reported as failed.
 
 Not included: 
 * Channel reserve: the required minimum reserve balance is not 

simln-lib/src/lib.rs

@@ -466,7 +466,9 @@ pub enum PaymentOutcome {
     NotDispatched,
     /// The payment was dispatched but its final status could not be determined.
     TrackPaymentFailed,
-    /// The payment failed at the provided index in the path.
+    /// The payment failed at the provided index in the path. Simulated nodes only report this for payments sent to
+    /// a specific route, which are not retried; payments that they route themselves report
+    /// [`PaymentOutcome::RetriesExhausted`] or [`PaymentOutcome::RouteNotFound`] instead.
     IndexFailure(usize),
 }