renepay: bug fix, local channel information

Listpeerchannels would update the local channel information setting the
liquidity in the outgoing channel to known_min=known_max=capacity,
when in fact it should be known_min=known_max=spendable.

plugins/renepay/mods.c

@@ -484,9 +484,13 @@ static void gossmod_cb(struct gossmap_localmods *mods,
 		payment_disable_chan(payment, scidd->scid, LOG_DBG,
 				     "listpeerchannels says not enabled");
 
-	/* Also update the uncertainty network */
-	uncertainty_update_from_listpeerchannels(pay_plugin->uncertainty, scidd, max,
-					      enabled, buf, chantok);
+	/* Also update the uncertainty network by fixing the liquidity of the
+	 * outgoing channel. If we try to set the liquidity of the incoming
+	 * channel as well we would have conflicting information because our
+	 * knowledge model does not take into account channel reserves. */
+	if (scidd->dir == node_id_idx(self, peer))
+		uncertainty_update_from_listpeerchannels(
+		    pay_plugin->uncertainty, scidd, max, enabled, buf, chantok);
 }
 
 static struct command_result *getmychannels_done(struct command *cmd,

tests/plugins/no_fail.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+"""Plugin that breaks the node if a fail notification is received.
+"""
+
+from pyln.client import Plugin, RpcError
+import os
+
+plugin = Plugin()
+
+
+@plugin.init()
+def init(plugin, options, configuration):
+    plugin.log("no_fail initialized")
+
+
+@plugin.subscribe("sendpay_failure")
+def channel_opened(plugin, sendpay_failure, **kwargs):
+    os._exit(1)
+
+
+@plugin.method("nofail")
+def nofail(plugin):
+    """Checks that the plugin is still running.
+    """
+    return {"status": "active"}
+
+
+plugin.run()

tests/test_renepay.py

@@ -435,11 +435,14 @@ def test_fee_allocation(node_factory):
     |    |
     3----4
     This a payment that fails if fee is not allocated as part of the flow
-    constraints.
+    constraints. The payment should be straightforward, no failures are
+    expected.
     """
-    # High fees at 3%
+    # We set high fees at 3% and load a plugin that breaks if a sendpay_failure
+    # notification is received.
     opts = [
-        {"disable-mpp": None, "fee-base": 1000, "fee-per-satoshi": 30000},
+        {"disable-mpp": None, "fee-base": 1000, "fee-per-satoshi": 30000,
+          'plugin': os.path.join(os.getcwd(), 'tests/plugins/no_fail.py')},
     ]
     l1, l2, l3, l4 = node_factory.get_nodes(4, opts=opts * 4)
     start_channels(
@@ -452,6 +455,9 @@ def test_fee_allocation(node_factory):
     invoice = only_one(l4.rpc.listinvoices("inv")["invoices"])
     assert invoice["amount_received_msat"] >= Millisatoshi("1500000sat")
 
+    # is the no_fail.py plugin still running?
+    l1.rpc.call("nofail")
+
 
 def test_htlc_max(node_factory):
     """