fix: deflake //rs/tests/message_routing/xnet:xnet_slo_120_subnets_staging_test_colocate

rs/tests/message_routing/xnet/slo_test_lib/xnet_slo_test_lib.rs

@@ -135,6 +135,11 @@ impl Config {
         config
     }
 
+    pub fn with_send_rate_threshold(mut self, send_rate_threshold: f64) -> Self {
+        self.send_rate_threshold = send_rate_threshold;
+        self
+    }
+
     pub fn with_payload_bytes(self, payload_size_bytes: u64) -> Self {
         let mut config = self.clone();
         config.request_payload_size_bytes = payload_size_bytes;

rs/tests/message_routing/xnet/xnet_slo_120_subnets_staging_test.rs

@@ -16,7 +16,14 @@ fn main() -> Result<()> {
     let config = Config::new(SUBNETS, NODES_PER_SUBNET, RUNTIME, REQUEST_RATE)
         // Only best-effort calls with 30 seconds timeout, so the test doesn't hang for
         // minutes in case we can't connect to some replica/subnet to pull.
-        .with_call_timeouts(&[Some(30)]);
+        .with_call_timeouts(&[Some(30)])
+        // With 120 single-node subnets colocated on shared performance hardware, the
+        // per-subnet block production rate varies between runs. On loaded runs a few
+        // "straggler" subnets dip just below the default 0.3 send rate threshold (down
+        // to ~0.28), while on unloaded runs the minimum is ~0.43. Lower the threshold to
+        // 0.2 to absorb this hardware variance while still catching systemic XNet
+        // regressions (the median send rate is ~0.7).
+        .with_send_rate_threshold(0.2);
     let test = config.clone().test();
 
     SystemTestGroup::new()