Merge branch 'refactor-node' into refactor-node-next

Forward-merge the dataplane/session concept-home reorganization onto
the next line. The moved files carry next's (XX-line) content; the one
hand-resolved surface is src/peer/active.rs, where the source-location
citation sits in different surrounding text than on the master line —
resolved by keeping next's body and applying the same node/session.rs
-> node/session/mod.rs citation update.

src/proto/routing/core.rs

@@ -1,7 +1,7 @@
 //! Sans-IO routing decision core.
 //!
 //! Pure, runtime-agnostic transit-forward decision for SessionDatagrams. The
-//! async I/O adapter in `node::handlers::forwarding` decodes the wire bytes,
+//! async I/O adapter in `node::dataplane::forwarding` decodes the wire bytes,
 //! pre-resolves the next hop, builds a [`RoutingView`] over live node state,
 //! calls [`Router::route`], and drives the returned [`RouteOutcome`] (the
 //! actual encrypted sends, metrics, and logging). No I/O, no clock, no

src/proto/routing/mod.rs

@@ -2,7 +2,7 @@
 //!
 //! Pure, runtime-agnostic routing state and decision core, migrated out of
 //! the async node shell. The async I/O handlers remain in
-//! `node::handlers::forwarding`.
+//! `node::dataplane::forwarding`.
 //!
 //! - `core.rs` — the `RoutingView` read-seam trait, the `NextHop` /
 //!   `RouteOutcome` types, `Router::route`, the pure transit-forward