Repoint the .NET E2E process cwd before deleting work directories

The in-process transport points the host process cwd at the context work
directory because the native worker inherits it. The assembly-level
isolation attribute only restores the cwd around tests that actually
execute, so the cwd could still reference a work directory that context
disposal then deleted. Every later Process.Start failed resolving its
executable because getcwd() returned ENOENT, cascading hundreds of
.NET E2E failures in the in-process matrix cells.

Repoint the cwd at its load-time value both before deleting the work
directory and before creating a new context.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 812b44f2-ef93-4b32-b051-c7092f612279

Author: stephentoub

dotnet/test/Harness/E2ETestContext.cs

@@ -40,6 +40,12 @@ private E2ETestContext(string homeDir, string workDir, string proxyUrl, ReplayPr
 
     public static async Task<E2ETestContext> CreateAsync()
     {
+        // A previous in-process context may have left this process's cwd inside a work
+        // directory that has since been deleted. getcwd() then fails, which breaks
+        // Process.Start below while it resolves the proxy executable. Repoint the cwd at
+        // the ambient value first; SetCurrentDirectory succeeds even if the old cwd is gone.
+        InProcessEnvIsolation.RestoreAmbientWorkingDirectory();
+
         var repoRoot = FindRepoRoot();
 
         var homeDir = Path.Combine(Path.GetTempPath(), $"copilot-test-config-{Guid.NewGuid()}");
@@ -478,6 +484,14 @@ public async ValueTask DisposeAsync()
         var isCI = !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("GITHUB_ACTIONS"));
         try { await _proxy.StopAsync(skipWritingCache: isCI); } catch (Exception ex) when (IsTransientCleanupException(ex)) { errors.Add(ex); }
 
+        // The in-process worker inherits this process's cwd, so ApplyInProcessEnvironment
+        // may have pointed it at WorkDir. The assembly-level isolation attribute only
+        // restores it around tests that actually execute, so a statically skipped test
+        // can leave the cwd inside a directory this method is about to delete. Every
+        // later Process.Start would then fail resolving its executable because getcwd()
+        // returns ENOENT. Repoint the cwd before deleting anything.
+        InProcessEnvIsolation.RestoreAmbientWorkingDirectory();
+
         try { await DeleteDirectoryAsync(HomeDir); } catch (Exception ex) when (IsTransientCleanupException(ex)) { errors.Add(ex); }
         try { await DeleteDirectoryAsync(WorkDir); } catch (Exception ex) when (IsTransientCleanupException(ex)) { errors.Add(ex); }
 

dotnet/test/Harness/InProcessEnvIsolation.cs

@@ -67,14 +67,22 @@ public static void NeutralizeAmbientCredentials()
     public static void SetWorkingDirectory(string path) =>
         Directory.SetCurrentDirectory(path);
 
+    // Repoints the process working directory at its load-time value. Callers must not
+    // read Directory.GetCurrentDirectory() first: an in-process test can chdir into a
+    // temp work dir that the harness then deletes, so getcwd() would throw
+    // FileNotFoundException. SetCurrentDirectory to an absolute path succeeds
+    // regardless of whether the old cwd still exists.
+    public static void RestoreAmbientWorkingDirectory() =>
+        Directory.SetCurrentDirectory(s_ambientCwd);
+
     public static void RestoreAmbient()
     {
         // Unconditionally repoint the process cwd at its load-time value. We must
         // not read Directory.GetCurrentDirectory() first: an in-process test can
         // chdir into a temp work dir that the harness then deletes, so getcwd()
         // would throw FileNotFoundException. SetCurrentDirectory to an absolute
         // path succeeds regardless of whether the old cwd still exists.
-        Directory.SetCurrentDirectory(s_ambientCwd);
+        RestoreAmbientWorkingDirectory();
 
         foreach (DictionaryEntry entry in Environment.GetEnvironmentVariables())
         {