TestFx acceptance validation

Produce evidence that the changed product ships correctly and that the intended regressions execute. A successful build, discovered tests, published TRX, or green job alone is not proof. Keep the work bounded to the changed contract.

Runtime choice

The Python execution gate is a measured exception to the repository's conditional PowerShell preference. A native PowerShell candidate did not meet the no-performance-regression condition for the documented standalone CLI path. On Windows with Python 3.12.10 and PowerShell 7.6.6, three warmups followed by 15 interleaved fresh-process samples per workload produced these medians, including process startup: