How a JSON Parse Error Masked a Critical Subprocess Failure in Python

A developer contributing to the open-source project Memanto discovered a subtle bug in a Python migration audit tool where a JSON parsing error was silently overriding a more meaningful subprocess failure. The tool ran a migration dry run and wrote a JSON fidelity receipt, but when the audit process crashed without producing valid JSON, the resulting JSONDecodeError surfaced instead of the original CalledProcessError and its exit code. This meant the actual cause of the operational failure was hidden from developers. The fix involved treating process success and JSON validity as two independent signals, ensuring that when JSON parsing fails alongside a process error, the original subprocess exception takes priority. A regression test was added to verify that the correct exception and exit code survive, and that invalid output is never written as an audit artifact.