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/mod.rs

@@ -1,6 +1,4 @@
 //! Canonical UnShell protocol modules.
-//!
-//! The wire model matches `PROTOCOL.md` directly.
 
 pub mod codec;
 pub mod introspection;
@@ -12,32 +10,14 @@ pub mod validation;
 mod tests;
 
 pub use codec::{
-    FrameBytes, FrameCodec, FrameError, ParsedFrame, RkyvCodec, deserialize_archived_bytes,
+    FrameBytes, FrameError, ParsedFrame, SECTION_ALIGN, decode_frame, deserialize_archived_bytes,
+    encode_packet,
+};
+pub use introspection::{
+    EndpointIntrospection, INTROSPECTION_PROCEDURE_ID, LeafIntrospection,
+    LeafIntrospectionSummary,
 };
-pub use introspection::{EndpointIntrospection, LeafIntrospection, LeafIntrospectionSummary};
 pub use types::{
     CallMessage, DataMessage, FaultMessage, HookTarget, PacketHeader, PacketType, ProtocolFault,
 };
 pub use validation::{ValidationError, validate_call, validate_header, validate_procedure_id};
-
-/// Encodes a header and payload with the crate's default frame codec.
-///
-/// This is a convenience wrapper around [`RkyvCodec`] for callers that do not
-/// need to choose a codec explicitly.
-pub fn encode_packet<P>(header: &PacketHeader, payload: &P) -> Result<FrameBytes, FrameError>
-where
-    P: for<'a> rkyv::Serialize<
-            rkyv::api::high::HighSerializer<
-                rkyv::util::AlignedVec,
-                rkyv::ser::allocator::ArenaHandle<'a>,
-                rkyv::rancor::Error,
-            >,
-        >,
-{
-    codec::encode_packet(header, payload)
-}
-
-/// Decodes a framed packet with the crate's default frame codec.
-pub fn decode_frame(bytes: &[u8]) -> Result<ParsedFrame<'_>, FrameError> {
-    codec::decode_frame(bytes)
-}