Clarify tree protocol runtime and routing

Document the hook lifecycle, ingress rules, and longest-prefix routing behavior so the tree endpoint code is easier to follow. Keep the pass behavior-neutral while tightening local names and comments around non-obvious protocol paths.

src/protocol/tree/endpoint/mod.rs

@@ -1,4 +1,8 @@
-//! Endpoint runtime and traits.
+//! Protocol-tree endpoint runtime.
+//!
+//! This module holds the state machine that validates ingress, decides whether a
+//! packet should be handled locally or forwarded, and manages hook lifetimes for
+//! call/data/fault exchanges.
 
 mod builders;
 mod core;