docs(v4.0.0): storage -- step 6 done

MESH.md step 6 as built, what is not as intended yet, and step 6b for
POST becoming the kernel's.  README and V3-PARITY.md brought up to date.

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

v4/README.md

@@ -126,11 +126,23 @@ no room for one more message lets it go and counts it in `(LOST)`.
 **Five nodes from nothing** (`MESH.md` step 5) is built and proven in the
 fabric under test: Hera asks whoever holds the fabric for a node
 (`v4/src/manage.c`: `NODE-BORN`, `NODE-WIRE` and the rest), sends it the
-nucleus through the port that joins them, then FORTH-79 and POST a line at
-a time, and joins four such nodes in a square round her
+nucleus through the port that joins them, then FORTH-79 a line at a
+time, and joins four such nodes in a square round her
 (`capsules/v4/hera.4th`: `BIRTH`, `UNIT`). `v4/tests/test_host_unit.c`.
 The two products are not yet this: they become the five nodes at steps 8
 and 9.
+A node she births is not POSTed: POST is the kernel's, once, on Hera.
+
+**Blocks** (`MESH.md` step 6). A node asks its kernel for a block, as a v3
+VM does: `BLOCK` and its family keep two buffers, and the word beneath them
+writes a request to port 0 with the block's number and the buffer's address
+on the stack (`v4/include/v4/blocks.h`). `v4/system/blocks.c` serves it from
+the kernel's block subsystem, which is v3's (`v3/src/block_subsystem.c`):
+one chain, the same blocks at the same numbers for every node. A hosted
+program has the chain's fast RAM, blocks 1 to 2047. On bare metal the chain
+is fast RAM, the ramdrive and the virtio disk; the disk is read and not yet
+written, because nothing in v4 gives its owner's word that it may be
+formatted. Who may have which block is not checked yet.
 
 **This is still the lone node.** On bare metal `kernel_main.c` starts it
 before the fleet tables, beside the kernel's own system and not in the VM's