diff --git a/PolyPilot.Tests/RepoManagerTests.cs b/PolyPilot.Tests/RepoManagerTests.cs
index 4eb3f6083a..0814955ca7 100644
--- a/PolyPilot.Tests/RepoManagerTests.cs
+++ b/PolyPilot.Tests/RepoManagerTests.cs
@@ -3,6 +3,7 @@
 
 namespace PolyPilot.Tests;
 
+[Collection("BaseDir")]
 public class RepoManagerTests
 {
     [Theory]
@@ -99,10 +100,8 @@ public void Save_AfterFailedLoad_DoesNotOverwriteWithEmptyState()
             SetField(rm, "_loadedSuccessfully", false);
             SetField(rm, "_state", new RepositoryState());
 
-            // Override StateFile to our temp path
-            var stateFileField = typeof(RepoManager).GetField("_stateFile", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)!;
-            var originalValue = stateFileField.GetValue(null);
-            stateFileField.SetValue(null, stateFile);
+            // Redirect RepoManager to our temp dir (safe — uses the lock-protected setter)
+            RepoManager.SetBaseDirForTesting(tempDir);
             try
             {
                 // Save should be blocked — empty state after failed load
@@ -114,7 +113,7 @@ public void Save_AfterFailedLoad_DoesNotOverwriteWithEmptyState()
             }
             finally
             {
-                stateFileField.SetValue(null, originalValue);
+                RepoManager.SetBaseDirForTesting(TestSetup.TestBaseDir);
             }
         }
         finally
@@ -129,7 +128,6 @@ public void Save_AfterSuccessfulLoad_PersistsEmptyState()
         var rm = new RepoManager();
         var tempDir = Path.Combine(Path.GetTempPath(), $"repomgr-test-{Guid.NewGuid():N}");
         Directory.CreateDirectory(tempDir);
-        var stateFile = Path.Combine(tempDir, "repos.json");
 
         try
         {
@@ -138,21 +136,21 @@ public void Save_AfterSuccessfulLoad_PersistsEmptyState()
             SetField(rm, "_loadedSuccessfully", true);
             SetField(rm, "_state", new RepositoryState());
 
-            var stateFileField = typeof(RepoManager).GetField("_stateFile", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)!;
-            var originalValue = stateFileField.GetValue(null);
-            stateFileField.SetValue(null, stateFile);
+            // Redirect RepoManager to our temp dir (safe — uses the lock-protected setter)
+            RepoManager.SetBaseDirForTesting(tempDir);
             try
             {
                 // Save should proceed — load was successful, intentional empty state
                 InvokeSave(rm);
 
+                var stateFile = Path.Combine(tempDir, "repos.json");
                 var content = File.ReadAllText(stateFile);
                 Assert.Contains("Repositories", content);
                 Assert.DoesNotContain("test-1", content);
             }
             finally
             {
-                stateFileField.SetValue(null, originalValue);
+                RepoManager.SetBaseDirForTesting(TestSetup.TestBaseDir);
             }
         }
         finally
diff --git a/PolyPilot.Tests/TestIsolationGuardTests.cs b/PolyPilot.Tests/TestIsolationGuardTests.cs
index 1ce64308ce..2daa29eb15 100644
--- a/PolyPilot.Tests/TestIsolationGuardTests.cs
+++ b/PolyPilot.Tests/TestIsolationGuardTests.cs
@@ -40,6 +40,38 @@ public void BaseDir_PointsToTempDirectory()
         Assert.Contains("polypilot-tests-", CopilotService.BaseDir);
     }
 
+    [Fact]
+    public void RepoManager_StateFile_IsNotRealPolypilotDir()
+    {
+        // Access the static StateFile via reflection to verify it doesn't point to real path
+        var stateFileField = typeof(RepoManager).GetField("_stateFile",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)!;
+        // Force resolution by accessing Repositories (which calls EnsureLoaded -> Load -> StateFile)
+        var rm = new RepoManager();
+        _ = rm.Repositories;
+
+        var stateFile = (string?)stateFileField.GetValue(null);
+        var realReposJson = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
+            ".polypilot", "repos.json");
+
+        Assert.NotNull(stateFile);
+        Assert.NotEqual(realReposJson, stateFile);
+        Assert.DoesNotContain(Path.Combine(".polypilot", "repos.json"), stateFile);
+    }
+
+    [Fact]
+    public void RepoManager_BaseDir_MatchesTestSetupDir()
+    {
+        // Verify RepoManager resolves to the same test directory as CopilotService
+        var baseDirOverride = typeof(RepoManager).GetField("_baseDirOverride",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static)!;
+        var overrideValue = (string?)baseDirOverride.GetValue(null);
+
+        Assert.NotNull(overrideValue);
+        Assert.Equal(TestSetup.TestBaseDir, overrideValue);
+    }
+
     [Fact]
     public void TestSetup_ModuleInitializer_HasRun()
     {
diff --git a/PolyPilot/Services/CopilotService.Organization.cs b/PolyPilot/Services/CopilotService.Organization.cs
index 0a55976f04..2a448edadf 100644
--- a/PolyPilot/Services/CopilotService.Organization.cs
+++ b/PolyPilot/Services/CopilotService.Organization.cs
@@ -1108,7 +1108,7 @@ private void AddOrchestratorSystemMessage(string sessionName, string message)
     #region Orchestration Persistence (relaunch resilience)
 
     private static string? _pendingOrchestrationFile;
-    private static string PendingOrchestrationFile => _pendingOrchestrationFile ??= Path.Combine(PolyPilotBaseDir, "pending-orchestration.json");
+    private static string PendingOrchestrationFile { get { lock (_pathLock) return _pendingOrchestrationFile ??= Path.Combine(PolyPilotBaseDir, "pending-orchestration.json"); } }
 
     internal void SavePendingOrchestration(PendingOrchestration pending)
     {
diff --git a/PolyPilot/Services/CopilotService.cs b/PolyPilot/Services/CopilotService.cs
index 94a09a8229..2f88a0f9fd 100644
--- a/PolyPilot/Services/CopilotService.cs
+++ b/PolyPilot/Services/CopilotService.cs
@@ -40,11 +40,12 @@ public partial class CopilotService : IAsyncDisposable
     private string? _activeSessionName;
     private SynchronizationContext? _syncContext;
     
+    private static readonly object _pathLock = new();
     private static string? _copilotBaseDir;
-    private static string CopilotBaseDir => LazyInitializer.EnsureInitialized(ref _copilotBaseDir, GetCopilotBaseDir);
+    private static string CopilotBaseDir { get { lock (_pathLock) return _copilotBaseDir ??= GetCopilotBaseDir(); } }
     
     private static string? _polyPilotBaseDir;
-    private static string PolyPilotBaseDir => LazyInitializer.EnsureInitialized(ref _polyPilotBaseDir, GetPolyPilotBaseDir);
+    private static string PolyPilotBaseDir { get { lock (_pathLock) return _polyPilotBaseDir ??= GetPolyPilotBaseDir(); } }
     internal static string BaseDir => PolyPilotBaseDir;
 
     private static string GetCopilotBaseDir()
@@ -100,19 +101,19 @@ private static string GetPolyPilotBaseDir()
     }
 
     private static string? _sessionStatePath;
-    private static string SessionStatePath => _sessionStatePath ??= Path.Combine(CopilotBaseDir, "session-state");
+    private static string SessionStatePath { get { lock (_pathLock) return _sessionStatePath ??= Path.Combine(CopilotBaseDir, "session-state"); } }
 
     private static string? _activeSessionsFile;
-    private static string ActiveSessionsFile => _activeSessionsFile ??= Path.Combine(PolyPilotBaseDir, "active-sessions.json");
+    private static string ActiveSessionsFile { get { lock (_pathLock) return _activeSessionsFile ??= Path.Combine(PolyPilotBaseDir, "active-sessions.json"); } }
 
     private static string? _sessionAliasesFile;
-    private static string SessionAliasesFile => _sessionAliasesFile ??= Path.Combine(PolyPilotBaseDir, "session-aliases.json");
+    private static string SessionAliasesFile { get { lock (_pathLock) return _sessionAliasesFile ??= Path.Combine(PolyPilotBaseDir, "session-aliases.json"); } }
 
     private static string? _uiStateFile;
-    private static string UiStateFile => _uiStateFile ??= Path.Combine(PolyPilotBaseDir, "ui-state.json");
+    private static string UiStateFile { get { lock (_pathLock) return _uiStateFile ??= Path.Combine(PolyPilotBaseDir, "ui-state.json"); } }
 
     private static string? _organizationFile;
-    private static string OrganizationFile => _organizationFile ??= Path.Combine(PolyPilotBaseDir, "organization.json");
+    private static string OrganizationFile { get { lock (_pathLock) return _organizationFile ??= Path.Combine(PolyPilotBaseDir, "organization.json"); } }
 
     /// <summary>
     /// Override base directory for tests to prevent writing to real ~/.polypilot/.
@@ -120,18 +121,21 @@ private static string GetPolyPilotBaseDir()
     /// </summary>
     internal static void SetBaseDirForTesting(string path)
     {
-        Volatile.Write(ref _polyPilotBaseDir, path);
-        _activeSessionsFile = null;
-        _sessionAliasesFile = null;
-        _uiStateFile = null;
-        _organizationFile = null;
-        Volatile.Write(ref _copilotBaseDir, null);
-        _sessionStatePath = null;
-        _pendingOrchestrationFile = null;
+        lock (_pathLock)
+        {
+            _polyPilotBaseDir = path;
+            _activeSessionsFile = null;
+            _sessionAliasesFile = null;
+            _uiStateFile = null;
+            _organizationFile = null;
+            _copilotBaseDir = null;
+            _sessionStatePath = null;
+            _pendingOrchestrationFile = null;
+        }
     }
 
     private static string? _projectDir;
-    private static string ProjectDir => _projectDir ??= FindProjectDir();
+    private static string ProjectDir { get { lock (_pathLock) return _projectDir ??= FindProjectDir(); } }
 
     private static string FindProjectDir()
     {
diff --git a/PolyPilot/Services/RepoManager.cs b/PolyPilot/Services/RepoManager.cs
index 740f5d990a..51b3193987 100644
--- a/PolyPilot/Services/RepoManager.cs
+++ b/PolyPilot/Services/RepoManager.cs
@@ -11,12 +11,13 @@ namespace PolyPilot.Services;
 public class RepoManager
 {
     private static string? _baseDirOverride;
+    private static readonly object _pathLock = new();
     private static string? _reposDir;
-    private static string ReposDir => _reposDir ??= GetReposDir();
+    private static string ReposDir { get { lock (_pathLock) return _reposDir ??= GetReposDir(); } }
     private static string? _worktreesDir;
-    private static string WorktreesDir => _worktreesDir ??= GetWorktreesDir();
+    private static string WorktreesDir { get { lock (_pathLock) return _worktreesDir ??= GetWorktreesDir(); } }
     private static string? _stateFile;
-    private static string StateFile => _stateFile ??= GetStateFile();
+    private static string StateFile { get { lock (_pathLock) return _stateFile ??= GetStateFile(); } }
 
     /// <summary>
     /// Redirect all RepoManager paths to a test directory.
@@ -24,10 +25,13 @@ public class RepoManager
     /// </summary>
     internal static void SetBaseDirForTesting(string? path)
     {
-        Volatile.Write(ref _baseDirOverride, path);
-        Volatile.Write(ref _reposDir, null);
-        Volatile.Write(ref _worktreesDir, null);
-        Volatile.Write(ref _stateFile, null);
+        lock (_pathLock)
+        {
+            _baseDirOverride = path;
+            _reposDir = null;
+            _worktreesDir = null;
+            _stateFile = null;
+        }
     }
 
     private RepositoryState _state = new();
@@ -46,7 +50,8 @@ private void EnsureLoaded()
 
     private static string GetBaseDir()
     {
-        var over = Volatile.Read(ref _baseDirOverride);
+        // Called from within _pathLock — no Volatile.Read needed
+        var over = _baseDirOverride;
         if (over != null) return over;
         try
         {
@@ -71,9 +76,10 @@ public void Load()
         _loadedSuccessfully = false;
         try
         {
-            if (File.Exists(StateFile))
+            var stateFile = StateFile; // resolve once
+            if (File.Exists(stateFile))
             {
-                var json = File.ReadAllText(StateFile);
+                var json = File.ReadAllText(stateFile);
                 _state = JsonSerializer.Deserialize<RepositoryState>(json) ?? new RepositoryState();
             }
             _loadedSuccessfully = true;
@@ -98,9 +104,10 @@ private void Save()
         _loadedSuccessfully = true;
         try
         {
-            Directory.CreateDirectory(Path.GetDirectoryName(StateFile)!);
+            var stateFile = StateFile; // resolve once
+            Directory.CreateDirectory(Path.GetDirectoryName(stateFile)!);
             var json = JsonSerializer.Serialize(_state, new JsonSerializerOptions { WriteIndented = true });
-            File.WriteAllText(StateFile, json);
+            File.WriteAllText(stateFile, json);
         }
         catch (Exception ex)
         {