diff --git a/cardano-diffusion/changelog.d/20251007_150408_coot_net_sim_tracer.md b/cardano-diffusion/changelog.d/20251007_150408_coot_net_sim_tracer.md
new file mode 100644
index 00000000000..b62c123ce17
--- /dev/null
+++ b/cardano-diffusion/changelog.d/20251007_150408_coot_net_sim_tracer.md
@@ -0,0 +1,10 @@
+### Breaking
+
+- `diffusionSimulation`: removed tracer argument, no longer polymorphic in
+  monad - using `IOSim` only.  `diffusionSimulationM` is available but not
+  exported.
+
+### Non-Breaking
+
+- Testing improvements in net-sim.
+
diff --git a/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet.hs b/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet.hs
index 2b55260551e..3e4ac9f977b 100644
--- a/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet.hs
+++ b/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet.hs
@@ -309,38 +309,49 @@ traceFromList = Trace.fromList (MainReturn  (Time 0) (Labelled (ThreadId []) (Ju
 
 
 testWithIOSim :: (SimTrace Void -> Int -> Property)
+              -- ^ property to verify
               -> Int
+              -- ^ number of trace events to analyse
               -> AbsBearerInfo
+              -- ^ bearer configuration
               -> DiffusionScript
+              -- ^ sim-net configuration
               -> Property
-testWithIOSim f traceNumber bi ds =
+testWithIOSim prop traceNumber bi ds =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo bi)
                                 ds
-                                iosimTracer
       trace = runSimTrace sim
-   in labelDiffusionScript ds
-    $ counterexample (intercalate "\n" $
-        selectTraceEventsSay' $ Trace.take traceNumber trace)
-    --counterexample (Trace.ppTrace show (ppSimEvent 0 0 0) $ Trace.take traceNumber trace)
-    $ f trace traceNumber
+   in labelDiffusionScript ds $
+      -- we don't capture the time in the say trace, we add it here
+      counterexample (intercalate "\n" $ map (\(Time t, ev) -> show t <> " " <> ev) $
+        selectTraceEventsSayWithTime' $ Trace.take traceNumber trace) $
+      -- counterexample (Trace.ppTrace show (ppSimEvent 0 0 0) $ Trace.take traceNumber trace) $
+      prop trace traceNumber
 
 
 testWithIOSimPOR :: (SimTrace Void -> Int -> Property)
+                 -- ^ property to verify
                  -> Int
+                 -- ^ number of trace events to analyse
                  -> AbsBearerInfo
+                 -- ^ bearer configuration
                  -> DiffusionScript
+                 -- ^ sim-net configuration
                  -> Property
-testWithIOSimPOR f traceNumber bi ds =
+testWithIOSimPOR prop traceNumber bi ds =
   let sim :: forall s . IOSim s Void
       sim = do
         exploreRaces
         diffusionSimulation (toBearerInfo bi)
                             ds
-                            iosimTracer
    in labelDiffusionScript ds
-    $ exploreSimTrace id sim $ \_ ioSimTrace ->
-        f ioSimTrace  traceNumber
+    $ exploreSimTrace id sim $ \_ trace ->
+        -- we don't capture the time in the say trace, we add it here
+        counterexample (intercalate "\n" $ map (\(Time t, ev) -> show t <> " " <> ev) $
+          selectTraceEventsSayWithTime' $ Trace.take traceNumber trace) $
+        -- counterexample (Trace.ppTrace show (ppSimEvent 0 0 0) $ Trace.take traceNumber trace) $
+        prop trace traceNumber
 
 
 --
@@ -489,9 +500,8 @@ unit_cm_valid_transitions =
                 ]
             ]
       sim :: forall s. IOSim s Void
-      sim = do
-        exploreRaces
-        diffusionSimulation (toBearerInfo bi) ds iosimTracer
+      sim = diffusionSimulation (toBearerInfo bi) ds
+
   in exploreSimTrace (\a -> a { explorationReplay = Just s }) sim $ \_ ioSimTrace ->
        prop_diffusion_cm_valid_transition_order' ioSimTrace short_trace
 
@@ -551,7 +561,6 @@ unit_connection_manager_trace_coverage =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo absNoAttenuation)
                                 script
-                                iosimTracer
 
       events :: [CM.Trace
                   NtNAddr
@@ -661,7 +670,6 @@ unit_connection_manager_transitions_coverage =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo absNoAttenuation)
                                 script
-                                iosimTracer
       trace = runSimTrace sim
 
       -- events from `traceTVar` installed in `newMutableConnState`
@@ -785,7 +793,6 @@ prop_inbound_governor_trace_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [IG.Trace NtNAddr]
       events = mapMaybe (\case DiffusionInboundGovernorTrace st -> Just st
@@ -943,8 +950,7 @@ prop_txSubmission_allTransactions (ArbTxDecisionPolicy decisionPolicy)
          ]
    in checkAllTransactions (runSimTrace
                               (diffusionSimulation noAttenuation
-                                                   diffScript
-                                                   iosimTracer)
+                                                   diffScript)
                            )
                            500_000 -- ^ Running for 500k might not be enough.
   where
@@ -1044,7 +1050,6 @@ prop_check_inflight_ratio bi ds@(DiffusionScript simArgs _ _) =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo bi)
                                 ds
-                                iosimTracer
 
       events :: Events DiffusionTestTrace
       events = Signal.eventsFromList
@@ -1088,7 +1093,6 @@ prop_inbound_governor_transitions_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [IG.RemoteTransitionTrace NtNAddr]
       events = mapMaybe (\case DiffusionInboundGovernorTransitionTrace st ->
@@ -1120,7 +1124,6 @@ prop_fetch_client_state_trace_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [TraceFetchClientState BlockHeader]
       events = mapMaybe (\case DiffusionFetchTrace st ->
@@ -1281,7 +1284,9 @@ prop_only_bootstrap_peers_in_fallback_state ioSimTrace traceNumber =
                        <*> govLedgerStateJudgement
                        <*> trIsNodeAlive
               )
-       in counterexample (List.intercalate "\n" $ map show $ Signal.eventsToList events)
+       in counterexample
+            (List.intercalate "\n" $
+              map (show . uncurry WithTime) $ Signal.eventsToList events)
         $ signalProperty 20 show
             Set.null
             keepNonTrustablePeersTooLong
@@ -1509,7 +1514,6 @@ prop_server_trace_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [Server.Trace NtNAddr]
       events = mapMaybe (\case DiffusionServerTrace st -> Just st
@@ -1538,7 +1542,6 @@ prop_peer_selection_action_trace_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [PeerSelectionActionsTrace NtNAddr NtNVersion]
       events = mapMaybe (\case DiffusionPeerSelectionActionsTrace st -> Just st
@@ -1597,7 +1600,6 @@ prop_peer_selection_trace_coverage defaultBearerInfo diffScript =
   let sim :: forall s . IOSim s Void
       sim = diffusionSimulation (toBearerInfo defaultBearerInfo)
                                 diffScript
-                                iosimTracer
 
       events :: [TracePeerSelection Cardano.ExtraState
                                     PeerTrustable
@@ -2815,7 +2817,11 @@ prop_diffusion_target_established_local ioSimTrace traceNumber =
               id
               promotionOpportunities
 
-       in counterexample
+       in
+          -- counterexample
+          --   (List.intercalate "\n"
+          --     (map (show . uncurry WithTime) $ eventsToList events))
+          counterexample
             ("\nSignal key: (local root peers, est. local peers, in progress promotions, " ++
              "recent failures, opportunities, ignored too long)\n"
             )
@@ -2997,7 +3003,10 @@ prop_diffusion_target_active_below ioSimTrace traceNumber =
               id
               promotionOpportunities
 
-       in counterexample
+       in
+          -- counterexample
+          --   (List.intercalate "\n" $ map (show . uncurry WithTime) $ Signal.eventsToList events) $
+          counterexample
             ("\nSignal key: (local, established peers, active peers, " ++
              "recent failures, opportunities, is node running, ignored too long)") $
           signalProperty 20 show
@@ -3166,12 +3175,13 @@ prop_diffusion_target_active_local_below ioSimTrace traceNumber =
               id
               promotionOpportunities
 
-       in counterexample
+       in
+          -- counterexample
+          --   (List.intercalate "\n" $
+          --     map (show . uncurry WithTime) $ Signal.eventsToList events) $
+          counterexample
             ("\nSignal key: (local, established peers, active peers, " ++
              "recent failures, opportunities, ignored too long)") $
-          -- counterexample
-          --   (List.intercalate "\n" $ map show $ Signal.eventsToList events) $
-
           signalProperty 20 show
             (\(_,_,_,_,_,toolong) -> Set.null toolong)
             ((,,,,,) <$> (LocalRootPeers.toGroupSets <$> govLocalRootPeersSig)
@@ -3308,7 +3318,7 @@ prop_diffusion_async_demotions ioSimTrace traceNumber =
             lastTime = fst
                      . last
                      $ evsList
-        in counterexample (unlines $ map show evsList)
+        in counterexample (unlines $ map (show . uncurry WithTime) evsList)
           $ classifySimulatedTime lastTime
           $ classifyNumberOfEvents (length evsList)
           $ verify_async_demotions ev
@@ -3534,11 +3544,11 @@ prop_diffusion_target_active_local_above ioSimTrace traceNumber =
               id
               demotionOpportunities
 
-       in counterexample
+       in
+         -- counterexample (List.intercalate "\n" $ map (show . uncurry WithTime) $ Signal.eventsToList events) $
+         counterexample
             ("\nSignal key: (local peers, active peers, " ++
              "demotion opportunities, ignored too long)") $
-          --counterexample (List.intercalate "\n" $ map show $ Signal.eventsToList events) $
-
           signalProperty 20 show
             (\(_,_,_,toolong) -> Set.null toolong)
             ((,,,) <$> (LocalRootPeers.toGroupSets <$> govLocalRootPeersSig)
@@ -3975,7 +3985,6 @@ prop_unit_reconnect =
       sim = diffusionSimulation (toBearerInfo (absNoAttenuation { abiInboundAttenuation  = SpeedAttenuation SlowSpeed (Time 20) 1000
                                                                 } ))
                                 diffScript
-                                iosimTracer
 
       events :: [Events (WithName NtNAddr DiffusionTestTrace)]
       events = Trace.toList
@@ -4272,7 +4281,6 @@ unit_peer_sharing =
     let sim :: forall s. IOSim s Void
         sim = diffusionSimulation (toBearerInfo absNoAttenuation)
                                   script
-                                  iosimTracer
 
         -- TODO: we need `CardanoTracePeerSelection addr` type alias!
         events :: Map NtNAddr [TracePeerSelection Cardano.ExtraState
@@ -4862,7 +4870,7 @@ unit_local_root_diffusion_mode :: DiffusionMode
 unit_local_root_diffusion_mode diffusionMode =
     -- this is a unit test
     withMaxSuccess 1 $
-    let sim = diffusionSimulation (toBearerInfo absNoAttenuation) script iosimTracer
+    let sim = diffusionSimulation (toBearerInfo absNoAttenuation) script
 
         -- list of negotiated version data
         events :: [NtNVersionData]
diff --git a/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet/Simulation.hs b/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet/Simulation.hs
index 2f3b4888247..bb54b757666 100644
--- a/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet/Simulation.hs
+++ b/cardano-diffusion/tests/lib/Test/Cardano/Network/Diffusion/Testnet/Simulation.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE BlockArguments        #-}
+{-# LANGUAGE DerivingVia           #-}
 {-# LANGUAGE FlexibleContexts      #-}
 {-# LANGUAGE GADTs                 #-}
 {-# LANGUAGE LambdaCase            #-}
@@ -28,7 +29,6 @@ module Test.Cardano.Network.Diffusion.Testnet.Simulation
     -- * Tracing
   , DiffusionTestTrace (..)
   , ppDiffusionTestTrace
-  , iosimTracer
     -- * Re-exports
   , TestAddress (..)
   , RelayAccessPoint (..)
@@ -48,7 +48,7 @@ import Control.Monad.Class.MonadThrow
 import Control.Monad.Class.MonadTime.SI
 import Control.Monad.Class.MonadTimer.SI
 import Control.Monad.Fix
-import Control.Monad.IOSim (IOSim, traceM)
+import Control.Monad.IOSim (IOSim)
 import Control.Tracer (Tracer (..), contramap, nullTracer, traceWith)
 
 import Data.Bifunctor (first)
@@ -998,18 +998,18 @@ ppDiffusionTestTrace (DiffusionDNSTrace tr)                         = show tr
 ppDiffusionTestTrace (DiffusionMuxTrace tr)                         = show tr
 
 
--- | A debug tracer which embeds events in DiffusionTestTrace.
+-- | Run an arbitrary topology in `IOSim`.
 --
-iosimTracer :: forall s.
-               Tracer (IOSim s) (WithTime (WithName NtNAddr DiffusionTestTrace))
-iosimTracer =
-     Tracer traceM
-  <> Tracer (\WithTime { wtEvent = WithName { wnName, wnEvent } } ->
-              -- don't log time, it's in the trace
-              say $ ppNtNAddr wnName ++ " @ " ++ ppDiffusionTestTrace wnEvent)
-
--- | Run an arbitrary topology
 diffusionSimulation
+  :: BearerInfo
+  -> DiffusionScript
+  -> IOSim s Void
+diffusionSimulation bearerInfo diffusionScript =
+  diffusionSimulationM bearerInfo diffusionScript dynamicTracer
+
+-- | Run an arbitrary topology in a generic monad `m`.
+--
+diffusionSimulationM
   :: forall m. ( Alternative (STM m)
                , MonadAsync       m
                , MonadDelay       m
@@ -1032,7 +1032,7 @@ diffusionSimulation
   -> Tracer m (WithTime (WithName NtNAddr DiffusionTestTrace))
   -- ^ timed trace of nodes in the system
   -> m Void
-diffusionSimulation
+diffusionSimulationM
   defaultBearerInfo
   (DiffusionScript simArgs dnsMapScript nodeArgs)
   nodeTracer = do
@@ -1046,11 +1046,11 @@ diffusionSimulation
         dnsMapVar <- fromLazyTVar <$> playTimedScript nullTracer dnsMapScript
         withAsyncAll
           (zipWith
-            (\(args, commands) i -> do
-              labelThisThread ("ctrl-" ++ ppNtNAddr (naAddr args))
-              runCommand ntnSnocket ntcSnocket dnsMapVar simArgs args connStateIdSupply i Nothing commands)
+            (\(args, commands) nodeId -> do
+              labelThisThread ("ctrl-" ++ show nodeId)
+              runCommand ntnSnocket ntcSnocket dnsMapVar simArgs args connStateIdSupply nodeId Nothing commands)
             nodeArgs
-            [1..])
+            [NodeId 1..])
           $ \nodes -> do
             (_, x) <- waitAny nodes
             return x
@@ -1070,7 +1070,7 @@ diffusionSimulation
       -> SimArgs -- ^ Simulation arguments needed in order to run a simulation
       -> NodeArgs -- ^ Simulation arguments needed in order to run a single node
       -> CM.ConnStateIdSupply m
-      -> Int
+      -> NodeId
       -> Maybe ( Async m Void
                , StrictTVar m [( HotValency
                                , WarmValency
@@ -1081,8 +1081,8 @@ diffusionSimulation
       -> [Command] -- ^ List of commands/actions to perform for a single node
       -> m Void
     runCommand ntnSocket ntcSocket dnsMapVar sArgs nArgs@NodeArgs { naAddr }
-               connStateIdSupply i hostAndLRP cmds = do
-      traceWith (diffSimTracer naAddr) . TrSay $ "node-" <> show i
+               connStateIdSupply nodeId hostAndLRP cmds = do
+      traceWith (diffSimTracer naAddr) . TrSay $ show nodeId ++ " @ " ++ ppNtNAddr naAddr
       runCommand' hostAndLRP cmds
       where
         runCommand' Nothing [] = do
@@ -1101,7 +1101,7 @@ diffusionSimulation
           threadDelay delay
           traceWith (diffSimTracer naAddr) TrJoiningNetwork
           lrpVar <- newTVarIO $ naLocalRootPeers nArgs
-          withAsync (runNode sArgs nArgs ntnSocket ntcSocket connStateIdSupply lrpVar dnsMapVar i) $ \nodeAsync ->
+          withAsync (runNode sArgs nArgs ntnSocket ntcSocket connStateIdSupply lrpVar dnsMapVar nodeId) $ \nodeAsync ->
             runCommand' (Just (nodeAsync, lrpVar)) cs
         runCommand' _ (JoinNetwork _:_) =
           error "runCommand: Impossible happened"
@@ -1135,7 +1135,7 @@ diffusionSimulation
                              , Map RelayAccessPoint (LocalRootConfig PeerTrustable)
                              )]
             -> StrictTVar m MockDNSMap
-            -> Int
+            -> NodeId
             -> m Void
     runNode SimArgs
             { saSlot                  = bgaSlotDuration
@@ -1162,7 +1162,8 @@ diffusionSimulation
             ntcSnocket
             connStateIdSupply
             lrpVar
-            dMapVar i = do
+            dMapVar
+            nodeId = do
       chainSyncExitVar <- newTVarIO chainSyncExitOnBlockNo
       ledgerPeersVar <- initScript' ledgerPeers
       onlyOutboundConnectionsStateVar <- newTVarIO UntrustedState
@@ -1308,7 +1309,7 @@ diffusionSimulation
               , Node.aTxs                  = txs
               }
 
-          tracers = mkTracers addr i
+          tracers = mkTracers addr nodeId
 
           requestPublicRootPeers' =
             requestPublicRootPeersImpl (Diffusion.dtTracePublicRootPeersTracer tracers)
@@ -1424,11 +1425,11 @@ diffusionSimulation
     diffSimTracer ntnAddr = contramap DiffusionSimulationTrace
                           . tracerWithName ntnAddr
                           . tracerWithTime
-                          $ nodeTracer <> sayTracer
+                          $ nodeTracer
 
     mkTracers
       :: NtNAddr
-      -> Int
+      -> NodeId
       -> Diffusion.Tracers NtNAddr NtNVersion NtNVersionData
                            NtCAddr NtCVersion NtCVersionData
                            Cardano.ExtraState
@@ -1437,17 +1438,24 @@ diffusionSimulation
                            (Cardano.ExtraPeerSelectionSetsWithSizes NtNAddr)
                            Cardano.ExtraTrace
                            m
-    mkTracers ntnAddr i =
-      let sayTracer' = Tracer \msg -> say $ "(node-" <> show i <> ")" <> show msg
-          -- toggle and uncomment interesting sayTracer' below
-          nodeTracer' = if True then nodeTracer <> sayTracer' else nodeTracer in
-
+    mkTracers ntnAddr nodeId =
+      let sayTracer' :: Show event => Tracer m event
+          sayTracer' = Tracer $ \event ->
+                       -- time of events is added in `testWithIOSim` and
+                       -- `testWithIOSimPOR`
+                       say $ show nodeId ++ " @ " ++ show event
+
+          nodeTracer' = nodeTracer
+                     <> sayTracer'
+                     -- DEBUG TIP: comment `sayTracer'` out to reduce noise and
+                     -- enable it below in one of the specific tracers
+      in
       Diffusion.nullTracers {
           -- Diffusion.dtMuxTracer = contramap
           --                           DiffusionMuxTrace
           --                       . tracerWithName ntnAddr
           --                       . tracerWithTime
-          --                       $ nodeTracer' -- <> sayTracer',
+          --                       $ nodeTracer
           Diffusion.dtTraceLocalRootPeersTracer  = contramap
                                                      DiffusionLocalRootPeerTrace
                                                  . tracerWithName ntnAddr
@@ -1480,8 +1488,8 @@ diffusionSimulation
                                                  . tracerWithName ntnAddr
                                                  . tracerWithTime
                                                  $ nodeTracer' -- <> sayTracer'
-        , Diffusion.dtTracePeerSelectionCounters = nullTracer
-        , Diffusion.dtTraceChurnCounters         = nullTracer
+        , Diffusion.dtTracePeerSelectionCounters = nullTracer -- <> sayTracer'
+        , Diffusion.dtTraceChurnCounters         = nullTracer -- <> sayTracer'
         , Diffusion.dtPeerSelectionActionsTracer = contramap
                                                      DiffusionPeerSelectionActionsTrace
                                                  . tracerWithName ntnAddr
@@ -1501,25 +1509,25 @@ diffusionSimulation
           -- * through `traceTVar` installed in `newMutableConnState`
           -- * the `dtConnectionManagerTransitionTracer`
                                                  $ nodeTracer' -- <> sayTracer'
-        , Diffusion.dtServerTracer          = contramap
-                                                DiffusionServerTrace
-                                            . tracerWithName ntnAddr
-                                            . tracerWithTime
-                                            $ nodeTracer' -- <> sayTracer'
-        , Diffusion.dtInboundGovernorTracer = contramap
-                                                DiffusionInboundGovernorTrace
-                                            . tracerWithName ntnAddr
-                                            . tracerWithTime
-                                            $ nodeTracer' -- <> sayTracer'
+        , Diffusion.dtServerTracer               = contramap
+                                                     DiffusionServerTrace
+                                                 . tracerWithName ntnAddr
+                                                 . tracerWithTime
+                                                 $ nodeTracer' -- <> sayTracer'
+        , Diffusion.dtInboundGovernorTracer      = contramap
+                                                     DiffusionInboundGovernorTrace
+                                                 . tracerWithName ntnAddr
+                                                 . tracerWithTime
+                                                 $ nodeTracer' -- <> sayTracer'
         , Diffusion.dtInboundGovernorTransitionTracer
                                                  = contramap
                                                      DiffusionInboundGovernorTransitionTrace
                                                  . tracerWithName ntnAddr
                                                  . tracerWithTime
                                                  $ nodeTracer' -- <> sayTracer'
-        , Diffusion.dtLocalConnectionManagerTracer = nullTracer
-        , Diffusion.dtLocalServerTracer            = nullTracer
-        , Diffusion.dtLocalInboundGovernorTracer   = nullTracer
+        , Diffusion.dtLocalConnectionManagerTracer = nullTracer -- <> sayTracer'
+        , Diffusion.dtLocalServerTracer            = nullTracer -- <> sayTracer'
+        , Diffusion.dtLocalInboundGovernorTracer   = nullTracer -- <> sayTracer'
         , Diffusion.dtDnsTracer                    = contramap DiffusionDNSTrace
                                                    . tracerWithName ntnAddr
                                                    . tracerWithTime
@@ -1544,6 +1552,13 @@ timeLimitsPingPong = ProtocolTimeLimits $ \case
 -- Utils
 --
 
+newtype NodeId = NodeId Int
+  deriving Enum via Int
+  deriving (Ord, Eq)
+
+instance Show NodeId where
+    show (NodeId n) = "node-" ++ show n
+
 withAsyncAll :: MonadAsync m => [m a] -> ([Async m a] -> m b) -> m b
 withAsyncAll xs0 action = go [] xs0
   where
diff --git a/ouroboros-network/changelog.d/20251007_150356_coot_net_sim_tracer.md b/ouroboros-network/changelog.d/20251007_150356_coot_net_sim_tracer.md
new file mode 100644
index 00000000000..aeedab97d0d
--- /dev/null
+++ b/ouroboros-network/changelog.d/20251007_150356_coot_net_sim_tracer.md
@@ -0,0 +1,6 @@
+### Non-Breaking
+
+- `PublicPeerSelectionState`: added `Show` instance.
+- `showSignalValue`: cleaner counterexample output.
+- `Test.Ouroboros.Network.Utils.dynamicTracer`: added, using  `IOSim`'s `traceM` API.
+
diff --git a/ouroboros-network/lib/Ouroboros/Network/PeerSelection/Governor/Types.hs b/ouroboros-network/lib/Ouroboros/Network/PeerSelection/Governor/Types.hs
index 30edf06971c..09c5e3717fc 100644
--- a/ouroboros-network/lib/Ouroboros/Network/PeerSelection/Governor/Types.hs
+++ b/ouroboros-network/lib/Ouroboros/Network/PeerSelection/Governor/Types.hs
@@ -772,6 +772,7 @@ newtype PublicPeerSelectionState peeraddr =
   PublicPeerSelectionState {
     availableToShare :: Set peeraddr
   }
+  deriving Show
 
 emptyPublicPeerSelectionState :: Ord peeraddr
                               => PublicPeerSelectionState peeraddr
diff --git a/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Data/Signal.hs b/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Data/Signal.hs
index ce96e7bdcd0..c0870f87168 100644
--- a/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Data/Signal.hs
+++ b/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Data/Signal.hs
@@ -541,12 +541,12 @@ signalProperty atMost showSignalValue p =
           | n < atMost = go (n+1) (              Deque.snoc (t,x)  recent) txs
           | otherwise  = go n     ((Deque.tail . Deque.snoc (t,x)) recent) txs
 
-    go !_ !recent ((t, x) : _) = counterexample details False
+    go !_ !recent ((Time t, x) : _) = counterexample details False
       where
         details =
           unlines [ "Last " ++ show atMost ++ " signal values:"
-                  , unlines [ show t' ++ "\t: " ++ showSignalValue x'
-                            | (t',x') <- Deque.toList recent ]
+                  , unlines [ show t' ++ "\t@ " ++ showSignalValue x'
+                            | (Time t',x') <- Deque.toList recent ]
                   , "Property violated at: " ++ show t
                   , "Invalid signal value:"
                   , showSignalValue x
diff --git a/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Utils.hs b/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Utils.hs
index 4a0bc844fa0..593f997d8f8 100644
--- a/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Utils.hs
+++ b/ouroboros-network/tests-lib/lib/Test/Ouroboros/Network/Utils.hs
@@ -36,6 +36,7 @@ module Test.Ouroboros.Network.Utils
   , debugTracer
   , debugTracerG
   , sayTracer
+  , dynamicTracer
     -- * Tasty Utils
   , nightlyTest
   , ignoreTest
@@ -185,6 +186,8 @@ data WithName name event = WithName {
 instance (Show name, Show event) => Show (WithName name event) where
   show (WithName name ev) = "#" <> show name <> " % " <> show ev
 
+-- NOTE: one shouldn't use it in `sayTracer`, use
+-- `selectTraceEventsSayWithTime` instead.
 data WithTime event = WithTime {
     wtTime  :: Time,
     wtEvent :: event
@@ -277,6 +280,9 @@ debugTracerG =    Tracer (\msg -> getCurrentTime >>= say . show . (,msg))
                <> Tracer traceM
             -- <> Tracer Debug.traceShowM
 
+dynamicTracer :: Typeable a => Tracer (IOSim s) a
+dynamicTracer = Tracer traceM
+
 --
 -- Nightly tests
 --
diff --git a/ouroboros-network/tests/lib/Test/Ouroboros/Network/BlockFetch.hs b/ouroboros-network/tests/lib/Test/Ouroboros/Network/BlockFetch.hs
index 4bccc937775..ae548e88ecc 100644
--- a/ouroboros-network/tests/lib/Test/Ouroboros/Network/BlockFetch.hs
+++ b/ouroboros-network/tests/lib/Test/Ouroboros/Network/BlockFetch.hs
@@ -23,7 +23,6 @@ import Data.Map qualified as Map
 import Data.Maybe (mapMaybe)
 import Data.Set (Set)
 import Data.Set qualified as Set
-import Data.Typeable (Typeable)
 
 import Control.Concurrent.Class.MonadSTM.Strict
 import Control.Exception (AssertionFailed (..), throw)
@@ -33,7 +32,7 @@ import Control.Monad.Class.MonadFork
 import Control.Monad.Class.MonadThrow
 import Control.Monad.Class.MonadTimer.SI
 import Control.Monad.IOSim
-import Control.Tracer (Tracer (Tracer), contramap, nullTracer)
+import Control.Tracer (contramap, nullTracer)
 
 import Ouroboros.Network.ControlMessage (ControlMessage (..))
 import Ouroboros.Network.DeltaQ
@@ -1002,11 +1001,3 @@ prop_comparePeerGSVEq salt p (PeerGSVT a) aActive =
     let peerSet = if aActive then Set.singleton p
                              else Set.empty in
     comparePeerGSV peerSet salt (a, p) (a, p) === EQ
-
-
---
--- Trace utils
---
-
-dynamicTracer :: Typeable a => Tracer (IOSim s) a
-dynamicTracer = Tracer traceM
diff --git a/ouroboros-network/tests/lib/Test/Ouroboros/Network/Diffusion/Node/Kernel.hs b/ouroboros-network/tests/lib/Test/Ouroboros/Network/Diffusion/Node/Kernel.hs
index 6ab63cd8955..e4beaea489c 100644
--- a/ouroboros-network/tests/lib/Test/Ouroboros/Network/Diffusion/Node/Kernel.hs
+++ b/ouroboros-network/tests/lib/Test/Ouroboros/Network/Diffusion/Node/Kernel.hs
@@ -322,7 +322,8 @@ data NodeKernel header block s txid m = NodeKernel {
         :: SharedTxStateVar m NtNAddr txid (Tx txid)
     }
 
-newNodeKernel :: ( MonadSTM m
+newNodeKernel :: ( MonadTraceSTM m
+                 , MonadLabelledSTM m
                  , Strict.MonadMVar m
                  , RandomGen rng
                  , Eq txid
@@ -333,6 +334,8 @@ newNodeKernel :: ( MonadSTM m
               -> m (NodeKernel header block rng txid m)
 newNodeKernel psRng txSeed txs = do
     publicStateVar <- makePublicPeerSelectionStateVar
+    labelTVarIO publicStateVar "public-peer-selection-state-var"
+    traceTVarIO publicStateVar (\_ a -> return $ TraceString (show a))
     NodeKernel
       <$> newTVarIO Map.empty
       <*> newTVarIO (ChainProducerState Chain.Genesis Map.empty 0)
@@ -422,6 +425,8 @@ withNodeKernelThread
      , MonadFork          m
      , MonadThrow         m
      , MonadThrow    (STM m)
+     , MonadTraceSTM      m
+     , MonadLabelledSTM   m
      , Strict.MonadMVar   m
      , HasFullHeader block
      , RandomGen seed