Load it at runtime. Know who signed it.

`plugin` is a small C++20 toolkit for applications that gain features from shared objects loaded at runtime. `dsold` opens the `.so` and keeps track of the handle; the `plugin::` templates let a loaded object register a factory by name so the host can create it without linking against it; and `plugin-sign` puts an Ed25519 signature and a manifest inside the DSO so the host can refuse anything a trusted key did not vouch for. Header-visible API, CMake / Conan, MIT.

A thread-safe DSO loader `DSOLoader::load` wraps `dlopen` with `RTLD_GLOBAL | RTLD_LAZY`, holds every handle for the process lifetime, and is guarded by a mutex. Load one file, a whole directory by extension, or every entry on `LD_LIBRARY_PATH`. A missing file throws `fedem::exception::FileNotFound`, not a crash.

Self-registering plugins A plugin `.cpp` drops in one `REGISTER(Circle, Shape)` line and, when its DSO loads, a `Circle` factory appears in `Shape`'s catalog. The host calls `Shape::create("Circle")` — or `create("Circle", Circle::Config{5})` for a typed config — without ever including `Circle.hh`.

Ed25519-signed add-ons `dso-sign` embeds a JSON manifest and a 64-byte signature as ELF sections. At load time `loadVerified` reports `TRUSTED` / `UNKNOWN` / `UNSIGNED` / `REJECTED` against a trusted-keys directory — the host decides the policy. No libelf; the check is mmap + a header walk.

C++20, CMake & Conan Builds standalone with CMake (≥ 3.20, GCC 12+), embeds via `add_subdirectory`, or comes in through Conan as three components — `dsold`, `plugin`, `plugin-sign`. OpenSSL is the only non-standard dependency, and only for the signing half. CPack produces 7Z / TGZ / ZIP / DEB / RPM.