Function manifest_filename_for_class 

pub fn manifest_filename_for_class(class_name: &str) -> String

Per-plugin manifest filename for a fully-qualified class name.

Plugins that share a package share one venv directory (it is keyed on the class root), but each needs its own manifest file: if pkg.a.PluginA and pkg.b.PluginB shared one, installing either would change the other’s manifest hash and both would rebuild forever.

Must produce byte-identical output to the Python side’s manifest_filename_for_class — both implementations resolve the same path, and a divergence means each sees the other’s install as a change.