feat(v4.0.0): a node is sent text as a message and sends back what it prints

MESH.md step 3.  The ports are the transport; the message is what is
transported: to, from, type, heat and TTL, ACL tag, sequence, length, then
text four characters to a word.

- quit.v4: a node with nothing to do is blocked reading "any port"; text
  for it is interpreted; (FINISH) sends what it printed and then how the
  text ended, and it waits again
- core.v4: EMIT keeps what is printed, (FLUSH-OUT) and (HDR) send it to the
  sender on the port the message came on.  EMIT still needs one free data
  cell and no more; it works on the return stack and in A and B
- message.h/.c: the same format for whatever is on a port and is not a node
- boot.c: the boot is the node's console on port 1 and its kernel on port 0
- the prompt tests are a console that speaks messages
- gone: v4_line_begin, v4_line_done, v4_line_status; writing a node's input
  buffer and setting its P from outside; any use of CONSOLE-TX

Verified: make -C v4 test (test_host_quit.c 1283 checks, the full-stack
figures unchanged) and make -C v4 sanitize pass; hosted-check passes on
three ISAs with POST 550 of 550; clean qemu with STARFORTH_V4=1 passes POST
and answers lines typed at each prompt on amd64, aarch64 and riscv64
(logs/20261006-110551, -111621, -111341).  -110837 is an aarch64 run ended
by the test wrapper's limit while still in UEFI firmware; it shows nothing
about v4.

Not done: KEY, EXPECT and QUERY still read the console's input registers;
a message not for this node is let go (step 4).

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

v4/tests/host_map.h

@@ -69,6 +69,12 @@
 #define CATCH        (BUF0_W - 8)               /* non-zero: a line's error is recorded here, -1, and the line ends " ok" */
 #define LINE_STATUS  (BUF0_W - 9)               /* how the last line ended: 0 QUIT, 1 completed, 2 an error */
 #define PORT         (BUF0_W - 32)              /* the node's ports (node.h): V4_PORTS of them, then "any port" and "which port".  Port 0 is where its requests go. */
+#define ME           (BUF0_W - 13)              /* this node's number: a message is for it when its first word is this */
+#define OUT_PTR      (BUF0_W - 14)              /* where the next character printed goes: a cell of the output buffer */
+#define REPLY        (BUF0_W - 15)              /* the address of the port the message being served came on */
+#define MSG          (BUF0_W - 48)              /* the header of the message being served, 7 cells */
+#define OUT_W        (BUF0_W - 400)             /* the output buffer: 256 cells, a character to a cell */
+#define OUT_CELLS    256
 #define WORD_DEFINED   (BUF0_W - 11)             /* the xt of the word that is told of each new entry, or 0 */
 #define WORD_FORGOTTEN (BUF0_W - 12)             /* the xt of the word that is told when entries go, or 0 */
 #define LOG_LEVEL    (BUF0_W - 5)               /* the level at or below which a message is printed */
@@ -108,6 +114,7 @@ static int host_load(v4_text *tx, v4_node *n, const char *const *files, unsigned
     unsigned i;
 
     v4_node_reset(n);
+    n->mem[OUT_PTR] = OUT_W;                 /* nothing has been printed: what is, is kept from here (core.v4) */
     v4_text_begin(tx, n, 16);
     v4_text_constant(tx, "N-1", V4_CELL_BITS - 1);
     v4_text_constant(tx, "NODE-ERROR", NODE_ERROR);
@@ -148,6 +155,11 @@ static int host_load(v4_text *tx, v4_node *n, const char *const *files, unsigned
     v4_text_constant(tx, "(CATCH)", CATCH);
     v4_text_constant(tx, "(LINE-STATUS)", LINE_STATUS);
     v4_text_constant(tx, "(PORT)", PORT);
+    v4_text_constant(tx, "(ME)", ME);
+    v4_text_constant(tx, "(OUT^)", OUT_PTR);
+    v4_text_constant(tx, "(REPLY)", REPLY);
+    v4_text_constant(tx, "(MSG)", MSG);
+    v4_text_constant(tx, "(OUT)", OUT_W);
     v4_text_constant(tx, "(WORD-DEFINED)", WORD_DEFINED);
     v4_text_constant(tx, "(WORD-FORGOTTEN)", WORD_FORGOTTEN);
     v4_text_constant(tx, "BLOCK-NUMBER", STORAGE_REG);