The review's portability warning: the six shell wrappers exec'd a bare
'python3', which /bin/sh resolves against its compiled-in default PATH while
the runtime spawns with env:{} — in environments where python3 is reachable
only through the caller's PATH (Nix, pyenv) every wrapper run would fail as
worker-exit. The wrappers now bake the resolved absolute interpreter path
(module-level resolvePythonBin, which the product spawn already uses), and
resolvePythonBin is exported for the tests.
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