node: Protect against non-monotonic clocks

Many (most?) system clocks are not monotonic, and even though we're
getting a `LocalTime`, which *is* monotonic when using `now()`, it is
constructed from a `SystemTime` which isn't.

Cargo.lock

@@ -1736,9 +1736,9 @@ checksum = "01cda141df6706de531b6c46c3a33ecca755538219bd484262fa09410c13539c"
 
 [[package]]
 name = "localtime"
-version = "1.3.0"
+version = "1.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "71c67b83b03434bb31132aef0b314b8a49a0db55ce195c7e3c29d27bbf003819"
+checksum = "016a009e0bb8ba6e3229fb74bf11a8fe6ef24542cc6ef35ef38863ac13f96d87"
 dependencies = [
  "serde",
 ]

radicle-node/src/service.rs

@@ -676,7 +676,17 @@ where
             "Tick +{}",
             now - self.started_at.expect("Service::tick: service must be initialized")
         );
+        if now >= self.clock {
             self.clock = now;
+        } else {
+            // Nb. In tests, we often move the clock forwards in time to test different behaviors,
+            // so this warning isn't applicable there.
+            #[cfg(not(test))]
+            warn!(
+                target: "service",
+                "System clock is not monotonic: {now} is not greater or equal to {}", self.clock
+            );
+        }
     }
 
     pub fn wake(&mut self) {