test_template_renders_python_invocation monkeypatches shutil.which to
return /usr/bin/python3, but on Windows resolve_python_interpreter guards
the which() result with a real _interpreter_runs subprocess probe (#3304).
The mocked /usr/bin/python3 path does not exist on a Windows runner, so the
probe fails, the resolver falls back to sys.executable (a ...python.exe
path), and the python3-anchored regex assertion fails.
Patch _interpreter_runs to return True in the _pin_interpreter fixture so
the resolved interpreter token stays python3 across all platforms, keeping
the #3304 production guard intact while making the assertion deterministic.
Assisted-by: GitHub Copilot (model: Claude Opus 4.8, autonomous)
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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