Source: src/firebird/driver/fbapi.py, relative to the repository root.
This is the low-level ctypes boundary. It defines Firebird C constants, structures, vtables,
and the FirebirdAPI loader. get_api() calls load_api() on first use; the loaded API
is cached in the module. An explicit filename or driver_config.fb_client_library.value
selects the client library before first load. The APIHook.LOADED callbacks run after initialization.
Changes to C layouts, pointer types, or signatures can affect every higher-level wrapper.
Compare them with the supported Firebird client API and run focused integration tests on
the affected Firebird versions. Preserve the initialization order used by interfaces.py
and core.py hooks.