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/README.md

@@ -146,9 +146,10 @@ is gone; a node believes that only from its centre.
 **The wait** (`MESH.md` 7c, step 6d). A node does not write the first word
 of a message: it offers it, and sleeps until it is taken or a word comes
 for it. What a node has to pass on, the answers it has to give and the
-refusals it owes all wait with it, offered, and go when they can. So a
-node that is stuck holds up no other: only text that must itself send to
-the stuck node waits, and on Hera a typed line ends that.
+refusals it owes all wait with it, offered, and go when they can. The aim
+is that a node that is stuck holds up no other. **It is not yet met in
+every case:** the review of step 6d found several where a node is still
+held or goes wrong, listed under step 6d in `MESH.md` section 10.
 
 **Blocks** (`MESH.md` step 6). The block words are the kernel's, as they
 are for a v3 VM: `BLOCK`, `BUFFER`, `UPDATE`, `SAVE-BUFFERS` and