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>

docs/v4.0.0/MESH.md

@@ -1256,6 +1256,37 @@ Each is tested, committed and pushed before the next.
      `hosted-check`, lint; three bare-metal boots, `logs/20261008-011558`
      (amd64), `-011833` (aarch64), `-012159` (riscv64). On all six: POST
      538 of 538, `word_count=317`, `dict_hash=0x6a39c0bb9d183418`.
+   - **The review (2026-10-08) found the step not sound as built.** One
+     finding is mended, the rest are open and the claims of 7b and 7c that
+     "a stuck node holds up no other" are not yet true in the cases below.
+     - *Mended.* A line that left 29 values on the stack hung the node for
+       ever, on the products too: the passes over the messages waiting
+       that now follow every text need four cells, and a stack fault in
+       the middle of one left the messages in pieces. Such a text now
+       ends "Stack overflow", as it did before step 6d
+       (`test_host_quit.c`; `hosted-check`). The boots above were made
+       before this and do not show it.
+     - *Open: a node removed while a message is being passed on to it*
+       leaves the node passing it on going round for ever: the error
+       comes in the middle of writing the message out of the messages
+       waiting, and leaves them in pieces.
+     - *Open: offers left standing.* When a node lets a message go and
+       then begins text without having slept, what it had offered is
+       still offered, and the text's own message can go to the wrong
+       port. The review saw text meant for one node done by another.
+     - *Open: what a finished text printed* is still begun as a message
+       from text is, and if the way to the console is through a stuck
+       node the node is held and cannot be typed to.
+     - *Open: with more than eight messages of its own waiting* (answers,
+       or the GONEs of `KILL`) a node begins no text at all; on Hera that
+       cannot be undone from the console.
+     - *Open, smaller:* an error while a refusal is being written leaves
+       a value on the stack; with no room at all, how text ended is
+       begun as a message and can be held by a stuck sender; a line that
+       was itself refused for want of room can still end a waiting text
+       "Interrupted"; a message a node makes itself may be passed on by
+       15 nodes, not 16; the flood's figures in 7a are stale (278 arrive
+       now) and `(LOST)` counts some messages more than once.
 
 7. **A second unit; scaling while running; sleep, wake and kill by
    command.**