fix(v4.0.0): 29 values left on the stack hung the node; and what the review of step 6d found

The review of step 6d found it not sound.  Mended here, with a check
that failed first: a text that left 29 values on the stack hung the
node for ever, on the products too -- the passes over the messages
waiting that follow every text need four cells, and a stack fault in the
middle of one left the messages in pieces.  Such a text ends 'Stack
overflow', as before step 6d.  hosted-check types it.

The other findings are open and are written under step 6d in MESH.md
section 10; the README no longer says the aim is met.

make -C v4 test and sanitize at both widths, hosted-check.  The bare
metal boots have not been made again.

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

v4/tests/test_host_quit.c

@@ -1134,6 +1134,21 @@ int main(void)
         }
         printf("  %u values may wait on the stack while the next line is typed and interpreted\n", most);
         CHECK(most + 4u >= V4_DATA_DEPTH, "the prompt and the interpreter take no more than four cells of the stack");
+        /* one more than may wait: the line ends in an error that says so, and the node goes on (found by the review of step 6d) */
+        {
+            char line[4 * V4_DATA_DEPTH + 16];
+            size_t at = 0;
+            unsigned m;
+            const char *r;
+            boot_bare();
+            for (m = 0; m < most + 1; m++) at += (size_t)snprintf(line + at, sizeof line - at, "1 ");
+            snprintf(line + at, sizeof line - at, "\n");
+            r = say(line);
+            CHECK(strstr(r, "Stack overflow") != NULL && strstr(r, " ERROR\nok> ") != NULL, "a line that leaves one value more than may wait ends in an error that says so: \"%s\"", r);
+            CHECK(strcmp(say("1 2 + .\n"), "3  ok\nok> ") == 0, "and the next line is done as usual");
+            for (m = 0; m < 2000 && !node_idle(); m++) (void)v4_exec_step_word(&n, &es, &h);   /* it finishes what it was doing when its answer went */
+            CHECK(n.mem[MQ_COUNT] == 0 && node_idle(), "with nothing left among the messages waiting, and the node at its ports");
+        }
     }
 
     /* ---- how much of the data stack a line has ---- */