fix: address CodeRabbit review feedback for Phase 13

- Use .get() to prevent KeyError when execution dict lacks 'error' key
- Use context manager for file read to prevent resource leak in test

src/services/statistical_analyzer.py

@@ -145,7 +145,9 @@ Generate executable Python code to analyze this evidence."""
                 return AnalysisResult(
                     verdict="INCONCLUSIVE",
                     confidence=0.0,
-                    statistical_evidence=f"Execution failed: {execution['error']}",
+                    statistical_evidence=(
+                        f"Execution failed: {execution.get('error', 'Unknown error')}"
+                    ),
                     code_generated=generated_code,
                     execution_output=execution.get("stderr", ""),
                     key_findings=[],

tests/unit/services/test_statistical_analyzer.py

@@ -38,7 +38,8 @@ class TestStatisticalAnalyzer:
         import src.services.statistical_analyzer as module
 
         # Check module doesn't import agent_framework
-        source = open(module.__file__).read()
+        with open(module.__file__) as f:
+            source = f.read()
         assert "from agent_framework" not in source
         assert "import agent_framework" not in source
         assert "BaseAgent" not in source