fix(task): reject unknown validation status payloads

app-instance/backend/tests/unit/test_task_mode_feedback.py

@@ -439,6 +439,11 @@ def test_validation_result_rejects_unknown_status() -> None:
         ValidationResult(status="pending", score=0.9, validator="test")  # type: ignore[arg-type]
 
 
+def test_validation_result_from_dict_rejects_unknown_explicit_status() -> None:
+    with pytest.raises(ValueError, match="unknown validation status"):
+        ValidationResult.from_dict({"status": "pending", "passed": True, "score": 0.9})
+
+
 def test_validation_result_evidence_gaps_round_trip() -> None:
     validation = ValidationResult(
         status="insufficient_evidence",