Rebuild protocol runtime from scratch

Implement an aligned two-section frame format, a compiled prefix router, a minimal pending and active hook engine, and a header-first receive path that only decodes payloads on local delivery. Recreate the protocol-focused test suite and document the explicit framing deviation in src/protocol/PROTOCOL_CHANGES.md.

src/protocol/tree/endpoint/mod.rs

@@ -1,14 +1,4 @@
 //! Endpoint runtime and traits.
-//!
-//! This module provides the core logic for a protocol endpoint, including
-//! packet ingress, routing decisions, and hook lifecycle management.
-//!
-//! Protocol section mapping:
-//! - `builders`: packet construction and outbound hook declaration
-//! - `receive`: framed ingress, authority checks, and route selection
-//! - `hooks`: hook lifecycle, peer validation, and fault emission
-//! - `introspection`: reserved empty-procedure discovery responses
-//! - `core`: externally visible endpoint state and result types
 
 mod builders;
 mod core;