diff --git a/chiasma-test.cabal b/chiasma-test.cabal
--- a/chiasma-test.cabal
+++ b/chiasma-test.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           chiasma-test
-version:        0.11.0.0
+version:        0.12.0.0
 synopsis:       Testing tools for chiasma
 description:    See https://hackage.haskell.org/package/chiasma-test/docs/Chiasma-Test.html
 category:       Terminal
@@ -71,7 +71,7 @@
       ViewPatterns
   ghc-options: -fplugin=Polysemy.Plugin -Wall -Widentities -Wincomplete-uni-patterns -Wmissing-deriving-strategies -Wredundant-constraints -Wunused-type-patterns -Wunused-packages
   build-depends:
-      base <5
+      base ==4.*
     , bytestring
     , chiasma
     , chronos
@@ -85,11 +85,11 @@
     , polysemy-log
     , polysemy-plugin
     , polysemy-process
-    , polysemy-test
+    , polysemy-test >=0.6
     , polysemy-time
-    , prelate
+    , prelate ==0.9.*
     , text
-    , typed-process
+    , typed-process >=0.2
   mixins:
       base hiding (Prelude)
     , prelate (Prelate as Prelude)
@@ -146,15 +146,15 @@
       ViewPatterns
   ghc-options: -fplugin=Polysemy.Plugin -threaded -rtsopts -with-rtsopts=-N -Wall -Widentities -Wincomplete-uni-patterns -Wmissing-deriving-strategies -Wredundant-constraints -Wunused-type-patterns -Wunused-packages
   build-depends:
-      base <5
+      base ==4.*
     , chiasma
     , chiasma-test
     , hedgehog
-    , lens
+    , lens >=4
     , polysemy
     , polysemy-plugin
-    , polysemy-test
-    , prelate
+    , polysemy-test >=0.6
+    , prelate ==0.9.*
     , tasty
     , tasty-hedgehog
   mixins:
@@ -168,6 +168,7 @@
   main-is: Main.hs
   other-modules:
       Chiasma.Test.CaptureTest
+      Chiasma.Test.ConcurrentTest
       Chiasma.Test.FindTest
       Chiasma.Test.RenderTest
       Chiasma.Test.TmuxTest
@@ -212,17 +213,16 @@
       ViewPatterns
   ghc-options: -fplugin=Polysemy.Plugin -threaded -rtsopts -with-rtsopts=-N -Wall -Widentities -Wincomplete-uni-patterns -Wmissing-deriving-strategies -Wredundant-constraints -Wunused-type-patterns -Wunused-packages
   build-depends:
-      base <5
+      base ==4.*
     , chiasma
     , chiasma-test
     , hedgehog
-    , lens
     , path-io
     , polysemy
     , polysemy-chronos
     , polysemy-plugin
-    , polysemy-test
-    , prelate
+    , polysemy-test >=0.6
+    , prelate ==0.9.*
     , tasty
     , tasty-hedgehog
   mixins:
diff --git a/integration/Chiasma/Test/ConcurrentTest.hs b/integration/Chiasma/Test/ConcurrentTest.hs
new file mode 100644
--- /dev/null
+++ b/integration/Chiasma/Test/ConcurrentTest.hs
@@ -0,0 +1,153 @@
+module Chiasma.Test.ConcurrentTest where
+
+import qualified Conc
+import Conc (withAsyncGated_, withAsync_)
+import qualified Data.Text as Text
+import Data.Text (stripPrefix)
+import Exon (exon)
+import Gate (Gate, signal)
+import Polysemy.Test (Hedgehog, UnitTest, assert, (===))
+import qualified Queue
+import Queue (QueueResult (..))
+import qualified Time
+import Time (MilliSeconds (MilliSeconds))
+
+import Chiasma.Codec.Data.Window (Window (..))
+import Chiasma.Data.CodecError (CodecError)
+import Chiasma.Data.TmuxCommand (TmuxCommand (ListWindows, NewWindow))
+import Chiasma.Data.TmuxError (TmuxError)
+import Chiasma.Data.TmuxNotification (TmuxNotification (..))
+import qualified Chiasma.Effect.TmuxApi as TmuxApi
+import Chiasma.Effect.TmuxApi (Tmux)
+import Chiasma.Effect.TmuxClient (NativeTmux)
+import Chiasma.Test.Tmux (tmuxTest)
+import Chiasma.Tmux (withTmux)
+
+-- | Run a loop of create-window then list-windows commands, collecting results.
+worker ::
+  Members [Tmux, AtomicState [Text]] r =>
+  Text ->
+  Sem r ()
+worker label =
+  for_ @[] [1 .. 10 :: Int] \ i -> do
+    win <- TmuxApi.send (NewWindow def)
+    wins <- TmuxApi.send (ListWindows def)
+    atomicModify' (<> [[exon|#{label}-#{show i}: created @#{show win.windowId}, total #{show (length wins)}|]])
+
+-- | Stress test for concurrent TmuxClient access.
+-- Two threads run inside a single @withTmux@ scope, each sending 20 commands
+-- (10 iterations × create + list). The Lock in tmuxRequest serializes
+-- send+receive pairs, ensuring correct response routing.
+test_concurrent :: UnitTest
+test_concurrent =
+  tmuxTest do
+    restop @TmuxError @NativeTmux $ withTmux @TmuxCommand @CodecError do
+      restop @CodecError @Tmux do
+        Conc.interpretAtomic @[Text] [] do
+          withAsync_ (worker "A") (worker "B")
+          wins <- TmuxApi.send (ListWindows def)
+          log' <- atomicGet
+          for_ log' (embed . putStrLn . toString)
+          -- 10 windows from each thread + 1 initial = 21
+          length wins === 21
+
+-- | Test that tmux control mode notifications are captured and accessible
+-- via the ReceiveNotification action.
+--
+-- A background thread consumes notifications and writes them to a Queue.
+-- Three phases exercise different consumption patterns:
+-- 1. Send 3 requests, take from queue after each
+-- 2. Send 3 requests, take 3 after the last one
+-- 3. Run 3 concurrent threads that each send 3 requests, take 9 after all finish
+--
+-- All notifications are asserted to be valid (non-empty, starting with '%').
+test_notifications :: UnitTest
+test_notifications =
+  tmuxTest do
+    restop @TmuxError @NativeTmux $ withTmux @TmuxCommand @CodecError do
+      restop @CodecError @Tmux do
+        Conc.interpretQueueTB @TmuxNotification 64 do
+          Conc.interpretGates do
+            withAsyncGated_ consumeNotifications do
+              -- Phase 1: interleaved send/take
+              phase1 <- for @[] [1 .. 3 :: Int] \ _ -> do
+                void $ TmuxApi.send (NewWindow def)
+                Time.sleep (MilliSeconds 10)
+                takeNotifications 1
+              let notes1 = concat phase1
+              assertOrdered notes1
+
+              -- Phase 2: batch send, then batch take
+              for_ @[] [1 .. 3 :: Int] \ _ -> do
+                void $ TmuxApi.send (NewWindow def)
+                Time.sleep (MilliSeconds 10)
+              notes2 <- takeNotifications 3
+              assertOrdered notes2
+
+              -- Phase 3: concurrent senders, batch take
+              withAsync_ sender $ withAsync_ sender sender
+              notes3 <- takeNotifications 9
+              assertOrdered notes3
+
+              -- Global ordering: each phase's notifications should follow the previous
+              assertOrdered (notes1 <> notes2 <> notes3)
+  where
+    consumeNotifications ::
+      Members [Tmux, Queue TmuxNotification, Gate] r =>
+      Sem r ()
+    consumeNotifications = do
+      signal
+      forever do
+        n <- TmuxApi.receiveNotification
+        Queue.write n
+
+    sender ::
+      Members [Tmux, Time t d] r =>
+      Sem r ()
+    sender =
+      for_ @[] [1 .. 3 :: Int] \ _ -> do
+        void $ TmuxApi.send (NewWindow def)
+        Time.sleep (MilliSeconds 10)
+
+    takeNotifications ::
+      Member (Queue TmuxNotification) r =>
+      Int ->
+      Sem r [TmuxNotification]
+    takeNotifications n =
+      catMaybes <$> replicateM n takeOne
+
+    takeOne ::
+      Member (Queue TmuxNotification) r =>
+      Sem r (Maybe TmuxNotification)
+    takeOne =
+      Queue.readTimeout (MilliSeconds 500) <&> \case
+        Success a -> Just a
+        _ -> Nothing
+
+    assertOrdered ::
+      Member (Hedgehog IO) r =>
+      [TmuxNotification] ->
+      Sem r ()
+    assertOrdered notes = do
+      assert (not (null notes))
+      for_ notes \ n ->
+        assert (not (Text.null n.name))
+      assertNonDecreasing (mapMaybe notificationId notes)
+
+    assertNonDecreasing ::
+      Member (Hedgehog IO) r =>
+      [Int] ->
+      Sem r ()
+    assertNonDecreasing = \case
+      [] -> unit
+      [_] -> unit
+      a : b : rest -> do
+        assert (a <= b)
+        assertNonDecreasing (b : rest)
+
+    notificationId :: TmuxNotification -> Maybe Int
+    notificationId n =
+      listToMaybe n.args >>= extractId
+
+    extractId :: Text -> Maybe Int
+    extractId = readMaybe . toString <=< stripPrefix "@"
diff --git a/integration/Main.hs b/integration/Main.hs
--- a/integration/Main.hs
+++ b/integration/Main.hs
@@ -1,6 +1,7 @@
 module Main where
 
 import Chiasma.Test.CaptureTest (test_capture)
+import Chiasma.Test.ConcurrentTest (test_concurrent, test_notifications)
 import Chiasma.Test.FindTest (test_find)
 import Chiasma.Test.RenderTest (test_render)
 import Chiasma.Test.TmuxTest (test_tmux)
@@ -13,7 +14,9 @@
     integrationTest "basic tmux commands" test_tmux,
     integrationTest "find pane by ID" test_find,
     test_render,
-    integrationTest "capture pane content" test_capture
+    integrationTest "capture pane content" test_capture,
+    integrationTest "concurrent tmux access" test_concurrent,
+    integrationTest "tmux notifications" test_notifications
   ]
 
 main :: IO ()
diff --git a/lib/Chiasma/Test/Tmux.hs b/lib/Chiasma/Test/Tmux.hs
--- a/lib/Chiasma/Test/Tmux.hs
+++ b/lib/Chiasma/Test/Tmux.hs
@@ -145,7 +145,7 @@
   ]
 
 withTestTmux ::
-  Members [Test, Time t d, Log, Resource, Stop TmuxError, Error Text, Race, Async, Embed IO] r =>
+  Members [Test, Time t d, Log, Resource, Stop TmuxError, Error Text, Race, Async, Final IO, Embed IO] r =>
   TmuxTestConfig ->
   Sem (TestTmuxEffects ++ r) a ->
   Path Abs Dir ->