cnct+htlcswitch+invoices: report circuit key to invoice registry

Currently the invoice registry cannot tell apart the htlcs that pay to
an invoice. Because htlcs may also be replayed on startup, it isn't
possible to determine the total amount paid to an invoice.

This commit is a first step towards fixing that. It reports the circuit
keys of htlcs to the invoice registry, which forms the basis for
accurate invoice accounting.

contractcourt/channel_arbitrator.go

@@ -498,9 +498,7 @@ func (c *ChannelArbitrator) supplementResolver(resolver ContractResolver,
 		return c.supplementSuccessResolver(r, htlcMap)
 
 	case *htlcIncomingContestResolver:
-		return c.supplementSuccessResolver(
-			&r.htlcSuccessResolver, htlcMap,
-		)
+		return c.supplementIncomingContestResolver(r, htlcMap)
 
 	case *htlcTimeoutResolver:
 		return c.supplementTimeoutResolver(r, htlcMap)
@@ -514,6 +512,30 @@ func (c *ChannelArbitrator) supplementResolver(resolver ContractResolver,
 	return nil
 }
 
+// supplementSuccessResolver takes a htlcIncomingContestResolver as it is
+// restored from the log and fills in missing data from the htlcMap.
+func (c *ChannelArbitrator) supplementIncomingContestResolver(
+	r *htlcIncomingContestResolver,
+	htlcMap map[wire.OutPoint]*channeldb.HTLC) error {
+
+	res := r.htlcResolution
+	htlcPoint := res.HtlcPoint()
+	htlc, ok := htlcMap[htlcPoint]
+	if !ok {
+		return errors.New(
+			"htlc for incoming contest resolver unavailable",
+		)
+	}
+
+	r.htlcAmt = htlc.Amt
+	r.circuitKey = channeldb.CircuitKey{
+		ChanID: c.cfg.ShortChanID,
+		HtlcID: htlc.HtlcIndex,
+	}
+
+	return nil
+}
+
 // supplementSuccessResolver takes a htlcSuccessResolver as it is restored from
 // the log and fills in missing data from the htlcMap.
 func (c *ChannelArbitrator) supplementSuccessResolver(r *htlcSuccessResolver,