fix(v4.0.0): step 6c mended after its review -- what a stuck or gone node can and cannot hold up

The review of step 6c found it did not keep its rule.  Ruled: fix them
all; 16 hops.

- Paying a NACK no longer waits on a lower-numbered neighbour; a node
  that owes one does not sleep, and goes on taking in what it is sent.
- AWAIT looks first through the messages already waiting.
- A node waiting to write to a removed neighbour gets error 18: the
  word that says who is reading also says which ports have anything on
  them.
- A console line lets Hera go when she is blocked on the first word of
  a message (v4_fabric_interrupt_error, a device's `pending`).
- A refused answer is told to the node that waits, not the one that
  answered; one owed to the node itself goes to its own queue.
- A message is passed on by at most 16 nodes, then refused.
- A GONE is believed only when it says it is from the node's centre.
- Tests: the check that tested nothing is replaced; no room for a
  waiting sender; the limit that remains is tested as a limit.
- MESH.md 7b's rule reworded to what holds, 7b.7 says where it falls
  short; README likewise.

make -C v4 test, sanitize, hosted-check; three bare-metal boots.  POST
538 of 538, word_count=317, dict_hash=0xc0769523a47b7dc3 on all six.

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

v4/tests/test_host_quit.c

@@ -63,6 +63,7 @@ static v4_heat       h;
 static v4_text       tx;
 static v4_cell       w_key, w_key_end, w_fault, capsule_latest;
 static v4_cell       w_idle;             /* (IDLE): where the node waits for a message */
+static v4_cell       w_idle_end;         /* (PASS-ON): the word after it */
 static char          out[V4_CONSOLE_CAP + 1];
 
 /* STORAGE (MESH.md section 8).  The node asks its kernel for its blocks, and
@@ -199,7 +200,7 @@ static int        text_ended;            /* how the text ended, when it has */
 /* 1 if the node is where it waits for a message, with nothing given it. */
 static int node_idle(void)
 {
-    return n.reading && !n.given && n.read_port == V4_PORT_ANY && n.p > w_idle && n.p <= w_idle + 8;   /* in the first words of (IDLE), where it reads */
+    return n.reading && !n.given && n.read_port == V4_PORT_ANY && n.p > w_idle && n.p <= w_idle_end;   /* in (IDLE), where it reads */
 }
 
 /* Run until the text ends, or until it has been inside KEY with nothing to
@@ -278,7 +279,7 @@ static void boot_with(unsigned depth)
     for (i = 0; i < depth; i++) v4_dstack_push(&n.ds, (v4_cell)(0x5A000000 + i));
     v4_dstack_push(&n.ds, CANARY);
     v4_node_port_attach(&n, PORT);
-    v4_node_port_status(&n, 0, 1u | 1u << CONSOLE_PORT);   /* the kernel and the console take what is written when it is written */
+    v4_node_port_status(&n, 0, (1u | 1u << CONSOLE_PORT) * (1u + (1u << V4_PORTS)));   /* the kernel and the console take what is written when it is written */
     n.mem[WORD_DEFINED] = 0;                         /* no one is told of entries, until a test says so */
     n.mem[WORD_FORGOTTEN] = 0;
     known_n = 0;
@@ -292,7 +293,7 @@ static void boot_with(unsigned depth)
     line_open = 0;
     to_node.count = 0; to_sent = 0; from_node.count = 0;
     shown_len = 0; shown_dropped = 0;
-    for (i = 0; i < 8 && !n.reading; i++) (void)v4_exec_step_word(&n, &es, &h);   /* no message waits: it reads its ports, and is blocked */
+    for (i = 0; i < 64 && !n.reading; i++) (void)v4_exec_step_word(&n, &es, &h);   /* no message waits: it reads its ports, and is blocked */
 }
 static void boot(void) { boot_with(0); }
 /* The same with nothing at all on the data stack. */
@@ -869,6 +870,7 @@ int main(void)
     printf("  capsule: %ld words\n", (long)v4_text_here(&tx) - 16);
     if (failures) { printf("  %d checks, %d failures\n", checks, failures); return 1; }
     w_idle = v4_text_word(&tx, "(IDLE)");
+    w_idle_end = v4_text_word(&tx, "(PASS-ON)");       /* the word after (IDLE) in quit.v4 */
     w_key = v4_text_word(&tx, "KEY");
     w_key_end = v4_text_word(&tx, "CR");               /* the word after KEY in core.v4 */
     w_fault = v4_text_word(&tx, "(FAULTS)");