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/introspection.rs

@@ -9,26 +9,20 @@ pub const INTROSPECTION_PROCEDURE_ID: &str = "";
 /// Endpoint-wide introspection payload.
 #[derive(Archive, Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
 pub struct EndpointIntrospection {
-    /// Direct child path segments currently registered under this endpoint.
     pub sub_endpoints: Vec<String>,
-    /// Hosted leaves and their supported procedures.
     pub leaves: Vec<LeafIntrospectionSummary>,
 }
 
 /// Shared per-leaf discovery record.
 #[derive(Archive, Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
 pub struct LeafIntrospectionSummary {
-    /// Local leaf name.
     pub leaf_name: String,
-    /// Canonical procedure identifiers supported by the leaf.
     pub procedures: Vec<String>,
 }
 
 /// Leaf-specific introspection payload.
 #[derive(Archive, Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
 pub struct LeafIntrospection {
-    /// Local leaf name.
     pub leaf_name: String,
-    /// Canonical procedure identifiers supported by the leaf.
     pub procedures: Vec<String>,
 }