feat(v4.0.0): the block words are the kernel's -- v3's way in full

Ruled 2026-10-07.  BLOCK, BUFFER, UPDATE, SAVE-BUFFERS and EMPTY-BUFFERS
are each one kernel request on port 0, by block number only.  The node
has a window of four slots in its memory, as a v3 VM has; the kernel
copies blocks into it, keeps the record of which block is in which slot,
and decides when a block is written (v4/system/blocks.c).  The node keeps
no record and gives the kernel no address, so a request cannot overwrite
the node's code.  When a block is written stays FORTH-79's: UPDATE marks
it.  When the chain of devices changes the slots are let go, as in v3.

The window is 512 cells more than the two buffers were; the dictionary
space ends that much lower, at 13824.

MESH.md 8.5 had said, from the review, that a v3 VM's BLOCK is the
kernel's buffer.  It is not, and the section now says what was reported,
what v3 does, and what was ruled.

make -C v4 test, sanitize and hosted-check pass; amd64, aarch64 and
riscv64 boot, POST 538 of 538, the same hashes on all six:
logs/20261007-092835, -093112, -093456.

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

capsules/BLOCK_MAP.md

@@ -1,5 +1,5 @@
 # Capsule Block Manifest — Auto-generated
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+<!-- Generated by mkcapsule --manifest  2026-10-07T13:34:17Z -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
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