feat(v4.0.0): every node asks the kernel for its blocks; a born node is not POSTed

A block is a kernel request, as ENGINE.md 3.3 has it: the node puts the
block's number and the address of 256 cells on its stack and writes the
request to port 0, and the kernel leaves the status there.  The requests
are -1, read, and -2, write, the same for every node.  v4/system/blocks.c
serves them from the kernel's block subsystem, which is v3's.  The four
storage registers are gone from the engine.

The device that spoke block messages (4a505a15) is withdrawn with its
test and its message types: Captain Bob ruled on 2026-10-07 that it, a
node's own drive, and nodes with no storage had left the OS as designed
(docs/v4.0.0/MESH.md 8.5).

Hera no longer sends POST to the nodes she births: POST is the kernel's,
once.  Every node has its kernel on port 0; it serves a node's blocks and,
for Hera alone, her requests for nodes and capsules.

Bare metal: the node boots and is POSTed against POST's own block RAM,
and the kernel's chain -- fast RAM, the ramdrive, the virtio disk -- is
set up after POST and before the prompt, as on the v3 path.  The disk is
read and not written: nothing in v4 yet gives the owner's word that it
may be formatted.  A hosted program has the chain's fast RAM, as hosted
v3 has with no disk.  Error 17 is Storage refused.

make -C v4 test and sanitize pass at both widths; hosted-check passes on
three ISAs; amd64, aarch64 and riscv64 boot, POST 538 of 538, with the
typed session: logs/20261007-081603, -081839, -082226.  The hashes are
the same on all six.

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

kernel/src/kernel_main.c

@@ -459,6 +459,45 @@ void kernel_main(BootInfo *boot_info) {
     kernel_main_deep(boot_info);
 }
 
+#ifdef STARFORTH_V4
+/* THE BLOCK CHAIN, for the v4 node.  It asks this kernel for its blocks
+ * (v4/include/v4/blocks.h, docs/v4.0.0/MESH.md 8.3).  The chain is set up
+ * with the calls the v3 path makes and in its order -- fast RAM and the
+ * ramdrive, then PCI, then the virtio disk -- and, as there, after POST.
+ * What the v3 path does next with that disk is not done here, because it is
+ * Artemis's and Zuse's and v4 has neither yet: the genesis signature,
+ * Zuse's root key, and the owner's word that the disk may be formatted.
+ * Until an owner gives that word the subsystem reads the disk and will not
+ * write it. */
+static BootInfo *sk_v4_boot_info;
+static void sk_v4_block_chain(void)
+{
+    const size_t ram_size = (size_t)BLK_RAM_BLOCKS * BLK_FORTH_SIZE, krd_size = 1024u * 1024u;
+    uint8_t *blk_ram = (uint8_t *)kmalloc(ram_size);
+    uint8_t *krd     = (uint8_t *)kmalloc(krd_size);
+    static blkio_dev_t artemis_dev;
+    size_t i;
+
+    if (!blk_ram || !krd) {
+        console_println("StarForth v4: no memory for the block chain");
+        for (;;) { }
+    }
+    for (i = 0; i < krd_size; i++) krd[i] = 0;
+    if (capsule_blk_init(NULL, blk_ram, ram_size, krd) != 0) {
+        console_println("StarForth v4: the block chain could not be set up");
+        for (;;) { }
+    }
+    console_println("PCI: init...");
+    pci_init(sk_v4_boot_info->acpi_table);
+    if (virtio_blk_find_artemis(&artemis_dev) == 0) {
+        console_println("Artemis: virtio-blk attached");
+        blk_subsys_attach_device(&artemis_dev);
+    } else {
+        console_println("Artemis: no virtio-blk disk");
+    }
+}
+#endif
+
 /**
  * @brief Deep kernel initialisation — M5 heartbeat, M7 VM bootstrap, and REPL.
  *
@@ -519,8 +558,8 @@ static void kernel_main_deep(BootInfo *boot_info) {
     /* StarForth v4 at a single prompt (Kconfig STARFORTH_V4): one host node
      * of the F18-derived engine, in place of the v3 VM and everything below.
      * It does not return. */
-    (void)boot_info;
-    sk_v4_run();
+    sk_v4_boot_info = boot_info;
+    sk_v4_run(sk_v4_block_chain);
 #endif
 
 #ifdef STARFORTH_ENABLE_VM