//! MCP protocol-version constant shared across the crate.
/// MCP protocol revision advertised on the `initialize` handshake.
///
/// Pinned to the 2025-03-26 Streamable HTTP revision so the client's
/// declared version matches the transport the server actually
/// implements. The in-tree echo-server fixture and the conformance test
/// reference this single constant to guard against drift.
pub const MCP_PROTOCOL_VERSION: &str = "2025-03-26";