The Rust MPP SDK ( mpp-test-sdk on crates.io) implements the full Solana HTTP 402 payment flow in pure async Rust. No Solana SDK dependency. Ed25519 signing, base58, and compact-u16 transaction encoding — all from scratch with ed25519-dalek and num-bigint . Framework-agnostic server middleware via a ChargeResult enum. Why Rust and HTTP 402? Rust is increasingly the language of high-performance APIs, WebAssembly services, and systems that need both speed and correctness. If you're building something in Rust that serves data — and you want to charge per request without billing infrastructure — HTTP 402 on Solana is the natural fit. The challenge is that most HTTP 402 / Solana tooling targets TypeScript or Python. The Rust MPP SDK changes that: pure Rust, async-first, no cgo, no Solana SDK, no wallet binary — just tokio , reqwest , ed25519-dalek , and the Solana JSON-RPC.…