fix(validating): guard null fileResult from MCP before ParseInnerJson

Prevents NullReferenceException when MCP returns null for a test file path.
Logs a warning and marks compilation as failed instead of crashing.

Also simplify McpToolResult constructor calls in tests to positional args.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Aitomates

src/GsdOrchestrator.Tests/McpToolDispatcherSecondaryRateLimitTests.cs

@@ -25,7 +25,7 @@ public async Task CallAsync_SecondaryRateLimit_EntersBranchThenCancels()
         var client = Substitute.For<IMcpClient>();
         var callCount = 0;
         client.CallToolAsync(Arg.Any<string>(), Arg.Any<JsonObject>(), Arg.Any<CancellationToken>())
-              .Returns(ci =>
+              .Returns<Task<McpToolResult>>(ci =>
               {
                   callCount++;
                   throw new McpException("secondary rate limit hit", isTransient: true, isSecondaryRateLimit: true);

src/GsdOrchestrator.Tests/ReviewingStateErrorPathTests.cs

@@ -40,9 +40,9 @@ public async Task GetPr_ReturnsError_FallsBackAndCompletes()
     {
         var m = Substitute.For<IMcpClient>();
         m.CallToolAsync(Arg.Is<string>("get_pull_request"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
-         .Returns(Task.FromResult(new McpToolResult("err",isError:true)));
+         .Returns(Task.FromResult(new McpToolResult("err",true)));
         m.CallToolAsync(Arg.Is<string>("create_pull_request_review"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
-         .Returns(Task.FromResult(new McpToolResult("{}",isError:false)));
+         .Returns(Task.FromResult(new McpToolResult("{}",false)));
         var res = await Sut(m,LlmApprove()).ExecuteAsync(PrCtx(),CancellationToken.None);
         Assert.Equal(WorkflowState.Done,res.CurrentState);
     }
@@ -54,7 +54,7 @@ public async Task GetPr_ThrowsMcpException_FallsBackAndCompletes()
         m.CallToolAsync(Arg.Is<string>("get_pull_request"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
          .ThrowsAsync(new McpException("notfound",isTransient:false));
         m.CallToolAsync(Arg.Is<string>("create_pull_request_review"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
-         .Returns(Task.FromResult(new McpToolResult("{}",isError:false)));
+         .Returns(Task.FromResult(new McpToolResult("{}",false)));
         var res = await Sut(m,LlmApprove()).ExecuteAsync(PrCtx(),CancellationToken.None);
         Assert.Equal(WorkflowState.Done,res.CurrentState);
     }
@@ -95,7 +95,7 @@ public async Task SubmitReview_ReturnsError_ThrowsMcpException()
         m.CallToolAsync(Arg.Is<string>("get_pull_request"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
          .Returns(Task.FromResult(new McpToolResult("{\"title\":\"T\",\"body\":\"\"}",false)));
         m.CallToolAsync(Arg.Is<string>("create_pull_request_review"),Arg.Any<JsonObject>(),Arg.Any<CancellationToken>())
-         .Returns(Task.FromResult(new McpToolResult("fail",isError:true)));
+         .Returns(Task.FromResult(new McpToolResult("fail",true)));
         await Assert.ThrowsAsync<McpException>(()=>Sut(m,LlmApprove()).ExecuteAsync(PrCtx(),CancellationToken.None));
     }
 

src/GsdOrchestrator.Tests/States/ValidatingStateTests.cs

@@ -186,11 +186,12 @@ private static IMcpClient BuildMcpClientWithFileContent(string fileContent)
         var mcp = BuildMcpClientAhead();
         var base64 = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(fileContent));
         var json = string.Format("{{\"content\":\"{0}\"}}", base64);
+        var result = new McpToolResult(json, false);
         mcp.CallToolAsync(
             Arg.Is<string>("get_file_contents"),
             Arg.Any<JsonObject>(),
             Arg.Any<CancellationToken>())
-           .Returns(Task.FromResult(new McpToolResult(json, false)));
+           .Returns(_ => Task.FromResult(result));
         return mcp;
     }
 

src/GsdOrchestrator/Workflows/States/ValidatingState.cs

@@ -142,6 +142,13 @@ public async Task<GsdWorkflowContext> ExecuteAsync(GsdWorkflowContext ctx, Cance
                             ["ref"] = branch.BranchName
                         }, ct);
 
+                        if (fileResult is null)
+                        {
+                            _logger.LogWarning("Test file {Path} returned null from MCP", generatedTest.TestPath);
+                            testCompilationPassed = false;
+                            continue;
+                        }
+
                         var fileJson = fileResult.ParseInnerJson();
                         var b64 = fileJson?["content"]?.GetValue<string>()?.Replace("\n", "") ?? "";
                         var content = b64.Length > 0