fix(sprite): give full_setup's scene step the same refusal shape as the others

Steps 1-3 refuse through Stop(), which returns success/step/message/diagnostics.
A step-4 failure fell through to the success-shaped return with the flag
flipped, so it was the only refusal in the tool with no 'message' and no 'step' -
the reason lived only inside the diagnostics array. The existing test passed
because it asserted on that array; it now asserts on the message and the step
too, which is what let the shape drift in the first place.

The asset fields stay on the failure: by step 4 the slice, the clips and the
controller are all on disk, and the caller needs to know that.

Author: shutong-bot

MCPForUnity/Editor/Tools/Sprite2D/SpriteFullSetup.cs

@@ -136,9 +136,27 @@ public static object Run(JObject @params, SpriteDiagnosticBuilder diagnostics)
                 }
             }
 
+            // Shaped like the other three steps' refusals rather than like a success with the
+            // flag flipped: a step-4 failure used to be the one refusal in the tool carrying
+            // neither 'step' nor 'message', leaving the reason only inside the diagnostics
+            // array. The asset fields stay on it, because by this point steps 1-3 have written
+            // and the caller needs to know what is already on disk.
+            if (diagnostics.HasErrors)
+                return new
+                {
+                    success           = false,
+                    step              = "add_to_scene",
+                    message           = diagnostics.FirstError,
+                    sprite_path       = path,
+                    controller_path   = controller.path,
+                    state_count       = controller.stateCount,
+                    clip_count        = clips.Count,
+                    diagnostics       = diagnostics.Build(),
+                };
+
             return new
             {
-                success               = !diagnostics.HasErrors,
+                success               = true,
                 sprite_path           = path,
                 controller_path       = controller.path,
                 state_count           = controller.stateCount,

TestProjects/UnityMCPTests/Assets/Tests/EditMode/Tools/ManageSpriteTests.cs

@@ -1261,6 +1261,10 @@ public void FullSetup_RequestedSceneTargetMissing_IsNotReportedAsSuccess()
             Assert.IsFalse(result.Value<bool>("success"),
                 "an attachment that was asked for and did not happen is not a success");
             Assert.That(result["diagnostics"].ToString(), Does.Contain("SCENE_TARGET_NOT_FOUND"));
+            // Asserted on the message rather than only the diagnostics array, because reading
+            // the array was what let this refusal keep a shape no other refusal in the tool has.
+            Assert.AreEqual("add_to_scene", result.Value<string>("step"));
+            Assert.That(ErrorText(result), Does.Contain("NoSuchObject"));
         }
 
         [Test]