When toolchain matching is enabled, install_dev_deps resolves the target's
Python and provisions the venv against it (uv sync --extra dev --python <v>,
uv auto-downloads), then runs a runnability smoke (uv run pytest --collect-only)
and records {python, status} in a .git/.roboco-toolchain marker the gates read.
Precision over recall: only a pytest collection error (the interpreter-mismatch
signature) reports 'broken'; pytest-absent / timeout report 'unknown' so a gate
never blocks on an inconclusive smoke. Flag off => provisioning is unchanged.
