MCPG is a thin host; everything with a policy, an upstream, or a side-effect is a plugin loaded across a stable binary boundary. The entity model, the three runtimes, capabilities, signing, and trust — explained.

Every plugin that ships with MCPG — backends, identity providers, policy engines, tool-gates, transforms, observability sinks, payment rails, and infrastructure adapters — with its id, class, and what it does.

Write a plugin in Rust (cdylib) or as a WASM Component. Sign it, pack it, distribute it via OCI, and wire it into a gateway config.