//! OxiGate Plugin SDK — extension-point traits for building OxiGate plugins.
//!
//! **Pre-release placeholder.** Trait definitions are under design (E-10).
//! Stable API not yet available. See <https://oxigate.io> for updates.
//!
//! ## Planned extension points
//!
//! - `Middleware` — custom pre-request, post-response, and error-handling logic
//! - `ProviderAdapter` — custom LLM provider backends
//! - `CostCalculator` — custom pricing logic per model or provider
//! - `RoutingStrategy` — custom request routing logic
//! - `StorageBackend` — swap the default PostgreSQL storage layer
//! - `ExportSink` — push cost/metrics data to custom destinations
/// Returns the crate version string.