A meteoroid impact on an engine bell can easily rupture a coolant pipe. Or it can create an imperfection in the backing plate from where cracks can form. Or it can destroy an injector. All of these can be fatal.
Yet by design, the interior of an engine bell cannot have a micrometeoroid shield. So how do spacecraft such as the Shuttle, Soyuz, and other manned and unmanned spacecraft protect the interior faces of the engines, main or otherwise?
It does seem to be that the Shuttle pointed the main engines at Earth, and the Soyuz has a lid. Are these protective measures?