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/capsule/quit.v4

@@ -54,6 +54,11 @@ macro R-CLEAR   RSTACK-DEPTH b! a !b   endmacro
 \ stops compiling first; it is always jumped to, never called, by
 \ something that has emptied the return stack (or by a fault, which empties
 \ it).  (LINE-STATUS) keeps how the last text ended.
+\ A TEXT MAY LEAVE 28 VALUES ON THE STACK.  What a node does between texts
+\ -- (IDLE)'s passes over the messages waiting -- needs four cells of it,
+\ and a stack fault in the middle of a pass would leave those messages in
+\ pieces.  So a text that leaves more ends here in "Stack overflow", with
+\ the stack emptied, as a fault would end it.
 \ THE MESSAGE SAYING HOW IT ENDED is not written here: whoever sent the
 \ text may be stuck, and this node would wait on it.  It is put with the
 \ messages waiting and passed on from (IDLE), as any message for another
@@ -61,6 +66,7 @@ macro R-CLEAR   RSTACK-DEPTH b! a !b   endmacro
 \ another text from the same sender until it has gone ((MINE?)): so what
 \ one sender is told comes in the order the texts were done.
 : (FINISH) ( s -- )
+  DSTACK-DEPTH a! @  -30 +  -if OVER  drop                            \ what follows needs four cells of the stack: with
   1 (QUIET) a! !                                                      \ from here an error is not this text's: see (RAISED)
   (LINE-STATUS) b! dup !b
   (FLUSH-OUT)
@@ -73,6 +79,7 @@ macro R-CLEAR   RSTACK-DEPTH b! a !b   endmacro
   (MQ!)                                                               \ how it ended
   pop  if FRONT  -1 +  FOR  (MQ@) (MQ!)  NEXT  jump (IDLE)            \ and those go round behind it: it is the oldest
   FRONT: drop  jump (IDLE)
+  OVER: drop  0 DSTACK-DEPTH a! !  jump (D-OVER)                      \ more left on it than may wait, the text ends in that error
   FULL: drop                                                          \ no room at all: it is offered here, and the node waits
   (MSG)+1 a! @  (DONE-PORT) a! @  (GATE)
   3 (HDR)  4 !b  !b