diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 45ace8ed..07bf6af8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -146,6 +146,9 @@ jobs:
       run: |
         cd tests
 
+        # The two macOS runners share a home, and two stack builds recaching one snapshot's
+        # package db deadlock against each other.
+        export STACK_ROOT="$HOME/.stack-$RUNNER_NAME"
         export NIX_PATH=nixpkgs=$(nix run .#nixpkgsPath)
 
         export PATH=$(nix build --no-link .#stack --json | jq -r '.[0].outputs.out')/bin:$PATH
@@ -164,10 +167,15 @@ jobs:
         echo "Got TEST_ROOT: $TEST_ROOT"
         echo TEST_ROOT="$TEST_ROOT" >> $GITHUB_ENV
 
+        # The two macOS runners share a home, and two stack builds recaching one snapshot's
+        # package db deadlock against each other.
+        export STACK_ROOT="$HOME/.stack-$RUNNER_NAME"
         export NIX_PATH=nixpkgs=$(nix run .#nixpkgsPath)
         export PATH=$(nix build --no-link .#stack --json | jq -r '.[0].outputs.out')/bin:$PATH
+        export PATH=$(nix build --no-link .#direnv --json | jq -r '.[0].outputs.out')/bin:$PATH
 
-        stack run --nix --no-nix-pure -- \
+        direnv allow
+        direnv exec . stack run --nix --no-nix-pure -- \
           --print \
           --fixed-root "$TEST_ROOT" \
           --markdown-summary "$GITHUB_STEP_SUMMARY" \
diff --git a/tests/app/Spec/Tests.hs b/tests/app/Spec/Tests.hs
index d2c3873f..c0fec56c 100644
--- a/tests/app/Spec/Tests.hs
+++ b/tests/app/Spec/Tests.hs
@@ -5,7 +5,6 @@
 
 module Spec.Tests where
 
-import Control.Concurrent.QSem
 import Control.Monad
 import Control.Monad.Catch
 import Control.Monad.IO.Class
@@ -28,13 +27,11 @@ tests =
   introduceJupyterRunner $
   introduceJustBubblewrap $
   introduceBootstrapNixpkgs $
-    introduce' (defaultNodeOptions { nodeOptionsCreateFolder = False }) "Introduce parallel semaphore" parallelSemaphore getQSem (const $ return ()) $
+    withParallelLanesFromArgs getParallelism $
       $(getSpecFromFolder $ defaultGetSpecFromFolderOptions {
            getSpecCombiner = 'describeParallel
-           , getSpecIndividualSpecHooks = 'withParallelSemaphore
+           , getSpecIndividualSpecHooks = 'takeParallelLane
            })
-  where
-    getQSem = getCommandLineOptions >>= liftIO . newQSem . getParallelism
 
 
 -- * Parallelism stuff
@@ -43,7 +40,7 @@ getParallelism :: CommandLineOptions SpecialOptions -> Int
 getParallelism = optTestParallelism . optUserOptions
 
 describeParallel :: (
-  MonadBaseControl IO m, MonadIO m, MonadMask m, HasParallelSemaphore context
+  MonadBaseControl IO m, MonadIO m, MonadMask m
   ) => String -> SpecFree context m () -> SpecFree context m ()
 describeParallel s = (describe' (defaultNodeOptions { nodeOptionsRecordTime = False
                                                     , nodeOptionsVisibilityThreshold = 50 })) s
@@ -51,11 +48,4 @@ describeParallel s = (describe' (defaultNodeOptions { nodeOptionsRecordTime = Fa
                                                     , nodeOptionsVisibilityThreshold = 125
                                                     , nodeOptionsCreateFolder = False }))
 
-withParallelSemaphore :: forall context m. (
-  MonadBaseControl IO m, MonadIO m, MonadMask m, HasParallelSemaphore context
-  ) => FilePath -> SpecFree context m () -> SpecFree context m ()
-withParallelSemaphore _ = around' (defaultNodeOptions { nodeOptionsRecordTime = False
-                                                      , nodeOptionsVisibilityThreshold = 125
-                                                      , nodeOptionsCreateFolder = False }) "claim semaphore" $ \action -> do
-  s <- getContext parallelSemaphore
-  bracket_ (liftIO $ waitQSem s) (liftIO $ signalQSem s) (void action)
+
diff --git a/tests/src/TestLib/TH.hs b/tests/src/TestLib/TH.hs
index 7eb862f3..ff96eeb7 100644
--- a/tests/src/TestLib/TH.hs
+++ b/tests/src/TestLib/TH.hs
@@ -11,8 +11,10 @@ import UnliftIO.Exception
 
 findGitRoot :: FilePath -> IO (Maybe FilePath)
 findGitRoot dir = do
-  let gitDir = dir </> ".git"
-  doesDirectoryExist gitDir >>= \case
+  let gitPath = dir </> ".git"
+  -- In a worktree or submodule checkout, .git is a file pointing at the real gitdir.
+  isRoot <- (||) <$> doesDirectoryExist gitPath <*> doesFileExist gitPath
+  case isRoot of
     True -> return (Just dir)
     False -> do
       let parent = takeDirectory dir
diff --git a/tests/stack.yaml b/tests/stack.yaml
index c5a6f5b5..a3f5de3d 100644
--- a/tests/stack.yaml
+++ b/tests/stack.yaml
@@ -11,6 +11,13 @@ nix:
 system-ghc: true
 
 extra-deps:
+- git: https://github.com/codedownio/sandwich.git
+  # master branch
+  commit: 71f7ac9754fe6bf6a6856cb0b774c356bb8ed02d
+  subdirs:
+  - sandwich
+  - sandwich-contexts
+
 - git: https://github.com/codedownio/lsp.git
   # upgrade-monads-newest-jan2026 branch
   commit: c723f4a4fb99661c76b1356f8a839a0e266b0f32
diff --git a/tests/stack.yaml.lock b/tests/stack.yaml.lock
index ad241700..656fa660 100644
--- a/tests/stack.yaml.lock
+++ b/tests/stack.yaml.lock
@@ -4,6 +4,32 @@
 #   https://docs.haskellstack.org/en/stable/topics/lock_files
 
 packages:
+- completed:
+    commit: 71f7ac9754fe6bf6a6856cb0b774c356bb8ed02d
+    git: https://github.com/codedownio/sandwich.git
+    name: sandwich
+    pantry-tree:
+      sha256: a025fad1cfe3429e13a06e040846e9c0baee29178750ac2e9911542e83ae315d
+      size: 7057
+    subdir: sandwich
+    version: 0.3.1.0
+  original:
+    commit: 71f7ac9754fe6bf6a6856cb0b774c356bb8ed02d
+    git: https://github.com/codedownio/sandwich.git
+    subdir: sandwich
+- completed:
+    commit: 71f7ac9754fe6bf6a6856cb0b774c356bb8ed02d
+    git: https://github.com/codedownio/sandwich.git
+    name: sandwich-contexts
+    pantry-tree:
+      sha256: 40d6a71d61001e81690af04a504a69e4be0a328f413ac239a8c1f3ed19a3bfae
+      size: 1849
+    subdir: sandwich-contexts
+    version: 0.3.0.4
+  original:
+    commit: 71f7ac9754fe6bf6a6856cb0b774c356bb8ed02d
+    git: https://github.com/codedownio/sandwich.git
+    subdir: sandwich-contexts
 - completed:
     commit: c723f4a4fb99661c76b1356f8a839a0e266b0f32
     git: https://github.com/codedownio/lsp.git