docs(v4.0.0): step 6d as mended after its review; the boots on that code

MESH.md 4.1, 7a, 7c.2, 7c.3, 7c.4 and step 6d say what the code now does,
what the review found and how each was mended, and what is small and not
mended.  The README no longer says the aim is unmet; it says the mended
code has not been reviewed again.

Three bare-metal boots on 2cf37aab, typing 29 values on a line: POST 538
of 538, word_count=317, dict_hash=0xd41a6ac9448fff60 on all six.

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

v4/README.md

@@ -146,10 +146,12 @@ 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. 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.
+refusals it owes all wait with it, offered, and go when they can. So a
+node that is stuck holds up no other, within the limits `MESH.md` 7c.4
+states: text that must itself send to the stuck node waits, and a node
+begins no more text from a sender it cannot yet answer. A review found
+this unsound as first built; what it found is mended and listed under
+step 6d in `MESH.md` section 10, and has not been reviewed again.
 
 **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