🛡️ Sentinel: [MEDIUM] Fix runtime error information leakage in stem separation worker

.Jules/sentinel.md

@@ -0,0 +1,4 @@
+## 2023-10-25 - Prevent information leakage from uncaught exceptions
+**Vulnerability:** In Python backend tasks (like stem separation workers), a general `except Exception as error` block leaked the raw stack trace or file path contents into the user-facing IPC `runtime_error` message string by calling `str(error)` directly.
+**Learning:** Backend worker processes often fail on arbitrary external exceptions that can carry verbose inner details. Leaking these violates the 'Fail securely' rule.
+**Prevention:** Replace broad exception casting (like `str(error)`) with generalized static strings (e.g., 'An unexpected error occurred...'). Ensure all explicitly caught errors are intentionally formatted for public reporting, rather than directly coercing exception bodies.

services/analysis-engine/src/bandscope_analysis/api.py

@@ -840,8 +840,8 @@ def _stem_separation_worker(
         result_queue.put(("value_error", str(error)))
     except RuntimeError as error:
         result_queue.put(("runtime_error", str(error)))
-    except Exception as error:
-        result_queue.put(("runtime_error", str(error)))
+    except Exception:
+        result_queue.put(("runtime_error", "An unexpected error occurred during stem separation."))
 
 
 def _multiprocessing_context() -> mp.context.BaseContext:

services/analysis-engine/tests/test_api.py

@@ -848,18 +848,22 @@ def put(self, item: tuple[str, object]) -> None:
             self.items.append(item)
 
     cases = [
-        (FileNotFoundError("missing"), "file_not_found"),
-        (ValueError("bad media"), "value_error"),
-        (RuntimeError("oom"), "runtime_error"),
-        (Exception("unexpected"), "runtime_error"),
+        (FileNotFoundError("missing"), "file_not_found", "missing"),
+        (ValueError("bad media"), "value_error", "bad media"),
+        (RuntimeError("oom"), "runtime_error", "oom"),
+        (
+            Exception("unexpected"),
+            "runtime_error",
+            "An unexpected error occurred during stem separation.",
+        ),
     ]
 
-    for error, expected_kind in cases:
+    for error, expected_kind, expected_msg in cases:
         fake_queue = FakeQueue()
         with patch("bandscope_analysis.api.AudioStemSeparator") as separator_class:
             separator_class.return_value.separate.side_effect = error
             _stem_separation_worker("/tmp/audio.wav", fake_queue)
-        assert fake_queue.items == [(expected_kind, str(error))]
+        assert fake_queue.items == [(expected_kind, expected_msg)]
 
     fake_queue = FakeQueue()
     with patch("bandscope_analysis.api.AudioStemSeparator") as separator_class: