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The device that spoke block messages (4a505a15) is withdrawn with its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>

v4/system/boot.c

@@ -4,6 +4,7 @@
  * It is not part of the engine (v4/src): it needs the capsule directory,
  * which only a whole system has.
  */
+#include "v4/blocks.h"
 #include "v4/boot.h"
 #include "v4/message.h"
 #include "starkernel/capsule.h"
@@ -109,9 +110,9 @@ static void post_watch(char c)
 
 /* The boot is the node's neighbour on two of its ports.  On port 0 it is
  * the kernel: the node writes the number of a request there (ENGINE.md
- * 3.3).  On port 1 it is the console: it writes the node a message of text
- * and reads back messages of what the node printed and of how the text
- * ended (message.h). */
+ * 3.3) -- for a block (blocks.h), or for one of the host's words.  On port
+ * 1 it is the console: it writes the node a message of text and reads back
+ * messages of what the node printed and of how the text ended (message.h). */
 #define KERNEL_PORT  0u
 #define CONSOLE_PORT 1u
 #define CONSOLE_ID   1                   /* the console's number as a sender; the node's is 0 until it is given one */
@@ -130,7 +131,9 @@ int v4_boot_line(const v4_boot *b, const char *text, unsigned len)
         if (n->stopped) return V4_BOOT_LINE_STOPPED;
 
         if (n->asking && n->ask_port == KERNEL_PORT) {         /* a request: the kernel's turn */
-            if (b->serve && n->request >= 1 && n->request <= (v4_cell)b->word_count) {
+            if (v4_blocks_serve(n, n->request)) {              /* a block, as for any node */
+                v4_node_port_served(n);
+            } else if (b->serve && n->request >= 1 && n->request <= (v4_cell)b->word_count) {
                 b->serve(n, (unsigned)n->request);
                 v4_node_port_served(n);
             } else {
@@ -335,13 +338,13 @@ static int load_nucleus(const v4_boot *b)
 
 /* ---- the whole boot ------------------------------------------------------ */
 
-int v4_boot_run(const v4_boot *b, unsigned char *disk, unsigned blocks)
+int v4_boot_run(const v4_boot *b)
 {
     unsigned i;
 
     post_len = 0; post_seen = 0; post_clean = 0;
     /* a node is born with nothing in it, and is sent the nucleus */
-    if (!v4_image_born(b->n, b->es, b->h, b->im, disk, blocks)) {
+    if (!v4_image_born(b->n, b->es, b->h, b->im)) {
         say(b, "V4: the nucleus is not for this build of the engine\nPARITY:FAIL\nPOST: FAILED\n");
         return 0;
     }