docs(v4.0.0): talking nodes -- 2x2 + 1 central, six ports, scaling at run time

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/v4.0.0/ENGINE.md

@@ -281,6 +281,17 @@ Rulings on that step so far:
   The common SSD is the system-resident store, Artemis's disk
   (`FABRIC-2.md` F.16).
 
+- **The first set of nodes: "2x2 + 1 central".** Five: four in a 2x2,
+  and one in the middle. Read back to Captain Bob, and not corrected, as:
+  each outer node wired to its two grid neighbours and to the centre; the
+  centre wired to all four; the centre is Hera.
+- **A node has six ports, not four** — "A, as long as it can scale at
+  runtime adaptively." With four, the centre's are all taken by the outer
+  nodes and nothing is left for the common SSD or the console. Six is also
+  what a 12^3 grid needs. `DECOMPOSITION.md` section 6 is to be corrected.
+- **It must scale at run time, adaptively.** The number of nodes and their
+  wiring are not fixed when the system is built.
+
 The design of this step is being worked out by question and answer and is
 not written yet. Nothing of it is built.