Add L0 test for work directory validation failure path

src/Test/L0/Listener/RunnerL0.cs

@@ -1076,5 +1076,75 @@ public async Task TestRunnerEnableAuthMigrationByDefault()
                 Assert.True(hc.AllowAuthMigration);
             }
         }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Runner")]
+        public async Task RunCommand_ShouldReturnTerminatedError_WhenWorkDirCreationFails()
+        {
+            using (var hostCtx = new TestHostContext(this))
+            {
+                // Setup: arrange mocks and runner instance
+                var runnerInstance = new Runner.Listener.Runner();
+                hostCtx.SetSingleton<IConfigurationManager>(_configurationManager.Object);
+                hostCtx.SetSingleton<IJobNotification>(_jobNotification.Object);
+                hostCtx.SetSingleton<IMessageListener>(_messageListener.Object);
+                hostCtx.SetSingleton<IPromptManager>(_promptManager.Object);
+                hostCtx.SetSingleton<IConfigurationStore>(_configStore.Object);
+                hostCtx.SetSingleton<IRunnerServer>(_runnerServer.Object);
+                hostCtx.EnqueueInstance<IErrorThrottler>(_acquireJobThrottler.Object);
+
+                runnerInstance.Initialize(hostCtx);
+
+                // Create a file at the work directory path to block directory creation
+                string workPath = hostCtx.GetDirectory(WellKnownDirectory.Work);
+
+                // Clean up any existing directory first
+                if (Directory.Exists(workPath))
+                {
+                    Directory.Delete(workPath, recursive: true);
+                }
+
+                // Place a file where the work directory should be - this blocks Directory.CreateDirectory
+                string parentPath = Path.GetDirectoryName(workPath);
+                Assert.NotNull(parentPath);
+                Assert.NotEmpty(parentPath);
+                Directory.CreateDirectory(parentPath);
+
+                const string blockingFileContent = "test file blocking directory creation";
+                File.WriteAllText(workPath, blockingFileContent);
+
+                const int testPoolId = 12345;
+                const int testAgentId = 67890;
+
+                var runnerConfig = new RunnerSettings
+                {
+                    PoolId = testPoolId,
+                    AgentId = testAgentId
+                };
+
+                _configurationManager.Setup(m => m.LoadSettings()).Returns(runnerConfig);
+                _configurationManager.Setup(m => m.IsConfigured()).Returns(true);
+                _configStore.Setup(m => m.IsServiceConfigured()).Returns(false);
+
+                try
+                {
+                    // Execute: run the command which should fail during work dir validation
+                    var cmd = new CommandSettings(hostCtx, new string[] { "run" });
+                    int exitCode = await runnerInstance.ExecuteCommand(cmd);
+
+                    // Verify: should return TerminatedError code when dir creation fails
+                    Assert.Equal(Constants.Runner.ReturnCode.TerminatedError, exitCode);
+                }
+                finally
+                {
+                    // Cleanup: remove the blocking file
+                    if (File.Exists(workPath))
+                    {
+                        File.Delete(workPath);
+                    }
+                }
+            }
+        }
     }
 }