CI runner installs only `pytest pytest-asyncio pyyaml`; without the
molecule_runtime/a2a/claude_sdk_executor stubs, the new
test_provider_resolution.py fails to collect with
ModuleNotFoundError. test_adapter_prevalidate.py owned the same
shims via a per-file _install_stubs(), but two files maintaining
parallel stub copies eventually disagree on shape (BaseAdapter
needing install_plugins_via_registry, etc.).
Move the shim install + sys.path bump into tests/conftest.py so
every test module shares a single canonical stub set, collected
before any test imports adapter.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
