feat(v4.0.0): a node is handed a line -- ENGINE.md step 1

A v4 node no longer reads its own command line or prints a prompt.  Its
host puts a line of text in the node's input buffer and starts it at
(LINE); the node interprets it and stops at (IDLE), leaving in
(LINE-STATUS) how it ended: completed, an error, or QUIT.  The host says
" ok" or " ERROR" and prompts, as the kernel's REPL does for a v3 VM.  A
line may be 1024 characters, a block, as v3's.  Ruled 2026-10-05
(V3-PARITY.md 1b); design ENGINE.md 3.1.

- quit.v4: (REPL), the node's prompt loop, is gone; (LINE) (IDLE) (DONE)
- image.h/.c: v4_line_begin, v4_line_done, v4_line_status; the node is
  idle at switch-on
- boot.c: v4_boot_line, the one loop the hosted binary, the kernel and the
  capsule loader hand a line with; the code that took " ok" and the prompt
  back out of the node's output is gone
- hosted.c, sk_v4.c: the prompt and the line editing are the host's
- test_host_quit.c: the tests are the node's host; two tests of the old
  80-character prompt line now test a whole line, 1024 and 1025 characters

Verified: make -C v4 test passes at both widths; hosted-check passes on
three ISAs; clean qemu with STARFORTH_V4=1 on amd64, aarch64 and riscv64
passes POST (550 of 550) with the same hashes as hosted, and three lines
typed at each bare-metal prompt through the serial port are answered
correctly (logs/20261005-180922, -181152, -181541).

Still the lone node: kernel_main.c starts it before the fleet tables.

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

v4/tools/mkimage.c

@@ -4,7 +4,7 @@
  *
  * Runs on the build machine.  It assembles capsule/ *.v4 -- the nucleus,
  * docs/v4.0.0/NUCLEUS.md -- onto a host node with the memory map of
- * tests/host_map.h and starts the node at its prompt.  Then it writes every
+ * tests/host_map.h.  It runs nothing: it writes every
  * word of the node's memory that is not zero, and the addresses a loader
  * needs, as a C file.  No FORTH source is compiled here: what is not in the
  * nucleus is loaded from capsules when the system boots (v4/system/boot.c).
@@ -22,11 +22,8 @@
 #include "../tests/host_map.h"
 
 static v4_node       n;
-static v4_exec_state es;
-static v4_heat       h;
 static v4_text       tx;
 static v4_cell       w_key, w_key_end;
-static unsigned char disk[4 * V4_BLOCK_BYTES];
 
 static void die(const char *what, const char *detail)
 {
@@ -34,19 +31,6 @@ static void die(const char *what, const char *detail)
     exit(1);
 }
 
-/* run until the node has taken all its input and is waiting in KEY */
-static void run_until_waiting(void)
-{
-    long steps = 0;
-    unsigned idle = 0;
-    while (idle < 64) {
-        if (++steps > 200000000L) die("the node did not come back to its prompt", NULL);
-        if (n.stopped) die("the node stopped on a fault", NULL);
-        (void)v4_exec_step_word(&n, &es, &h);
-        if (n.input_pos == n.input_len && n.p >= w_key && n.p < w_key_end) idle++; else idle = 0;
-    }
-}
-
 /* every entry from xt back: no access control fields set */
 static void clear_acl(v4_cell xt)
 {
@@ -58,7 +42,7 @@ int main(int argc, char **argv)
     static const char *const files[] = { "core.v4", "input.v4", "dict.v4", "codegen.v4", "compile.v4", "quit.v4", "forth.v4",
                                          "numout.v4", "words.v4", "system.v4", "qmath.v4", "blocks.v4", "log.v4", "acl.v4" };
     FILE *out;
-    v4_cell k, entry, faults, voc;
+    v4_cell k, line, idle, faults, voc;
     unsigned count = 0;
 
     if (argc != 2) die("usage: mkimage OUTPUT.c", NULL);
@@ -66,7 +50,8 @@ int main(int argc, char **argv)
     if (!host_load(&tx, &n, files, (unsigned)(sizeof files / sizeof files[0]))) die("the capsule does not assemble", NULL);
     if (!v4_text_finish(&tx)) die("not everything is defined", v4_text_error(&tx));
     if (v4_text_here(&tx) >= DICT_W) die("the capsule's code runs into the dictionary space", NULL);
-    entry = v4_text_word(&tx, "QUIT");
+    line = v4_text_word(&tx, "(LINE)");
+    idle = v4_text_word(&tx, "(IDLE)");
     faults = v4_text_word(&tx, "(FAULTS)");
     w_key = v4_text_word(&tx, "KEY");
     w_key_end = v4_text_word(&tx, "CR");
@@ -83,16 +68,6 @@ int main(int argc, char **argv)
     n.mem[CURRENT] = LATEST;
     n.mem[SRC] = TIB;
 
-    v4_exec_reset(&es);
-    v4_heat_reset(&h);
-    v4_node_console_attach(&n, CONSOLE_TX);
-    v4_node_console_input_attach(&n, CONSOLE_RX, CONSOLE_ST);
-    v4_node_error_attach(&n, NODE_ERROR);
-    v4_node_fault_attach(&n, faults);
-    v4_node_storage_attach(&n, STORAGE_REG, disk, 4);
-    n.p = entry;
-    run_until_waiting();
-
     /* The nucleus is the system as COLD finds it: COLD comes back to here,
      * and FORGET will not go below it.  What the capsules add at boot
      * (v4/system/boot.c) is above it. */
@@ -125,7 +100,8 @@ int main(int argc, char **argv)
         }
     fprintf(out, "};\n\nconst v4_image v4_capsule_image = {\n    cells, %uu,\n    %uu, %uu, %uu, %uu,\n", count,
             (unsigned)V4_CELL_BITS, (unsigned)V4_NODE_WORDS, (unsigned)V4_DATA_RING, (unsigned)V4_RET_RING);
-    fprintf(out, "    %ld, %ld,\n    %ld, %ld,\n", (long)entry, (long)faults, (long)w_key, (long)w_key_end);
+    fprintf(out, "    %ld, %ld, %ld,\n    %ld, %uu, %ld,\n    %ld,\n    %ld, %ld,\n", (long)line, (long)idle, (long)LINE_STATUS,
+            (long)TIB, 1025u, (long)SPAN, (long)faults, (long)w_key, (long)w_key_end);
     fprintf(out, "    %ld, %ld, %ld,\n    %ld, %ld,\n    %ld,\n    %ld,\n    %ld, %ld\n};\n", (long)CONSOLE_TX, (long)CONSOLE_RX, (long)CONSOLE_ST,
             (long)DSTACK_REG, (long)RSTACK_REG, (long)NODE_ERROR, (long)STORAGE_REG, (long)DP, (long)LATEST);
     if (fclose(out) != 0) die("cannot write", argv[1]);