docs(v4.0.0): where v4 is going; the next step is talking nodes

Captain Bob, 2026-10-05: F18 engines digesting capsules, 12x12 then 12^3;
the next step is nodes talking and sharing the common SSD, ahead of v4 = v3
on bare metal.  Rulings so far: ports are the transport and v3's message is
what is transported; some nodes have storage of their own.

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

docs/v4.0.0/ENGINE.md

@@ -249,6 +249,41 @@ It is step 6's, and section 6 lists it as open.
 there is one node and nothing to share the processor with. It is not how
 the kernel will run a fleet, and goes with the lone node at step 5.
 
+## 3d. Where v4 is going, and the next step (Captain Bob, 2026-10-05)
+
+> The entire point is that ultimately we have F18 engines digesting
+> capsules alone, and in a sense can be anything written in F18 assembler
+> for our fabric — 144 someday as a 12x12 grid, but I want a 12^3 FPGA
+> ultimately, where using a capsule digester like StarForth, it's more
+> than an operating system.
+
+So the unit is an engine and the capsule it digests; StarForth is one
+digester. The engine in `v4/src` must stay free of anything specific to
+StarForth or to the kernel, and what is built to make v4 equal v3 on a PC
+(section 3b's records, v3's C functions serving requests) stays on the
+kernel's side. (12^3 is a three-dimensional grid: six neighbours.
+`DECOMPOSITION.md` section 6 has four ports. Noted, not ruled.)
+
+Asked whether v4 = v3 on bare metal comes first, or nodes talking to
+nodes: **"The next step is talking nodes sharing the common SSD, and [they]
+may or may not have block storage available."** Step 4 below waits.
+
+Rulings on that step so far:
+
+- **The ports are the transport; the message is what is transported.**
+  Node to node, a write blocks until the neighbour reads
+  (`DECOMPOSITION.md` section 6). What travels is v3's Hermes message with
+  what it carries — type, from, to, channel, heat and TTL, ACL tag, a
+  payload of FORTH text up to a block — so v3's messaging rules are not
+  dropped; they go with the message.
+- **Storage: some nodes have storage of their own** (a thumbdrive, as a
+  user's identity has today), in addition to or instead of the common SSD.
+  The common SSD is the system-resident store, Artemis's disk
+  (`FABRIC-2.md` F.16).
+
+The design of this step is being worked out by question and answer and is
+not written yet. Nothing of it is built.
+
 ## 4. What was built on the detour
 
 | Built 2026-10-05 | What becomes of it |