fix: remove hash key from EditResult on error

- Add model validator to set hash to None when result is "error"
- Improve to_dict method to exclude keys with None values
- Update test cases to verify new behavior

Author: Yoshihiro Takahara

src/mcp_text_editor/models.py

@@ -63,13 +63,21 @@ class EditResult(BaseModel):
         None, description="Current content hash (None for missing files)"
     )
 
+    @model_validator(mode="after")
+    def validate_error_result(self) -> "EditResult":
+        """Remove hash when result is error."""
+        if self.result == "error":
+            object.__setattr__(self, "hash", None)
+        return self
+
     def to_dict(self) -> Dict:
         """Convert EditResult to a dictionary."""
-        return {
-            "result": self.result,
-            "reason": self.reason,
-            "hash": self.hash,
-        }
+        result = {"result": self.result}
+        if self.reason is not None:
+            result["reason"] = self.reason
+        if self.hash is not None:
+            result["hash"] = self.hash
+        return result
 
 
 class EditTextFileContentsRequest(BaseModel):

tests/test_models.py

@@ -114,6 +114,10 @@ def test_edit_result():
     assert result.result == "ok"
     assert result.hash == "newhash123"
     assert result.reason is None
+    result_dict = result.to_dict()
+    assert result_dict["result"] == "ok"
+    assert result_dict["hash"] == "newhash123"
+    assert "reason" not in result_dict
 
     # Test error result with reason
     result = EditResult(
@@ -123,7 +127,11 @@ def test_edit_result():
     )
     assert result.result == "error"
     assert result.reason == "hash mismatch"
-    assert result.hash == "currenthash123"
+    assert result.hash is None
+    result_dict = result.to_dict()
+    assert result_dict["result"] == "error"
+    assert result_dict["reason"] == "hash mismatch"
+    assert "hash" not in result_dict
 
     # Test validation error - missing required fields
     with pytest.raises(ValidationError):
@@ -177,11 +185,7 @@ def test_edit_result_to_dict():
     # Test successful result
     result = EditResult(result="ok", hash="newhash123")
     result_dict = result.to_dict()
-    assert result_dict == {
-        "result": "ok",
-        "hash": "newhash123",
-        "reason": None,
-    }
+    assert result_dict == {"result": "ok", "hash": "newhash123"}
 
     # Test error result
     result = EditResult(
@@ -190,11 +194,7 @@ def test_edit_result_to_dict():
         hash="currenthash123",
     )
     result_dict = result.to_dict()
-    assert result_dict == {
-        "result": "error",
-        "reason": "hash mismatch",
-        "hash": "currenthash123",
-    }
+    assert result_dict == {"result": "error", "reason": "hash mismatch"}
 
 
 def test_file_range():