From de612dabd923f3d9fecec667accff7ab6e74ea22 Mon Sep 17 00:00:00 2001
From: Florent Tapponnier <160007691+Flotapponnier@users.noreply.github.com>
Date: Tue, 11 Aug 2026 13:10:40 +0200
Subject: [PATCH] fix(squid): use fee+gas sum when USD amounts cancel out on
 stable pairs

---
 .../bridge-monitor/cmd/monitor/squid_bridge.go      | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/harnesses/bridge-monitor/cmd/monitor/squid_bridge.go b/harnesses/bridge-monitor/cmd/monitor/squid_bridge.go
index afc962b8..e5772f69 100644
--- a/harnesses/bridge-monitor/cmd/monitor/squid_bridge.go
+++ b/harnesses/bridge-monitor/cmd/monitor/squid_bridge.go
@@ -169,7 +169,16 @@ func (s *SquidBridge) TestRoute(route TestRoute, amount, amountUsd float64, rawU
 		gasUsd += v
 	}
 
-	costUsd := inUsd - outUsd + gasUsd
+	// Prefer fromAmountUSD - toAmountUSD as the all-in cost (captures spread + fees + gas
+	// as netted by the router). Fall back to explicit fee+gas sum when the USD amounts
+	// are identical (e.g. stable→stable where spot prices cancel out).
+	diffUsd := inUsd - outUsd
+	var costUsd float64
+	if diffUsd > 0.001 {
+		costUsd = diffUsd
+	} else {
+		costUsd = bridgeFeeUsd + gasUsd
+	}
 	if costUsd < 0 {
 		costUsd = 0
 	}
@@ -177,7 +186,7 @@ func (s *SquidBridge) TestRoute(route TestRoute, amount, amountUsd float64, rawU
 	if amountUsd > 0 {
 		costPct = (costUsd / amountUsd) * 100
 	}
-	slippage := costUsd - bridgeFeeUsd - gasUsd
+	slippage := diffUsd - bridgeFeeUsd - gasUsd
 	if slippage < 0 {
 		slippage = 0
 	}