feat(v4.0.0): step 6e -- a node removed at any step leaves the rest at rest; written up

test_host_mesh.c, 220 checks: three exchanges on the row of three -- text
from the console for node 12 with what it prints and how it ended; node 11
SENDing node 12 text and waiting for its answer; a message node 12 has no
way for and its NACK to node 10 -- are each played once for every engine
step they take with node 11 removed at that step, and again with node 12:
17,642 removals at 64 bits.  Every node left comes to rest asleep, blocked
at no port and in no operation, and answers.  What is typed is a word
defined beforehand, so that the steps are the exchange's and not the
dictionary being searched.

Removed from the engine, nothing using them: v4_fabric_interrupt_error, a
device's pending hook, v4_node_words_since_look, V4_ERROR_INTERRUPTED.

MESH.md: 4.1's table has the addresses after the ports; 7a and 7b say what
of them still holds; 7b.7's limit is closed; step 6e is written up.
v4/README.md likewise.

make -C v4 test and sanitize at both widths, hosted-check, lint.  Three
bare-metal boots with the typed session and a loop printing 400 numbers:
logs/20261013-165124 (amd64), -165428 (aarch64), -165818 (riscv64).  POST
538 of 538, word_count=317, dict_hash=0x0951d7e02e251554 on all six, and
the three sessions are the same character for character.  The boots were
built with the working tree's uncommitted change to kernel/Makefile that
adds the ISA to the kernel's version line; nothing else differs from this
commit.

The plan's final review is not done yet.

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

v4/include/v4/node.h

@@ -120,7 +120,6 @@ typedef struct {
     unsigned      last_from;         /* the port the last read from "any" took its word from */
     unsigned      writers;           /* bit k: the neighbour on port k is blocked writing to this node */
     unsigned      readers;           /* bit k: the neighbour on port k is blocked reading from this node */
-    unsigned      since_look;        /* words taken from this node since it last fetched either of those */
 
     /* Whole messages on the wires (MESH.md 7d.3).  See v4_node_port_attach. */
     unsigned      wire;              /* the port that A, B and Do are about; V4_PORTS if what was stored is not a port */
@@ -262,13 +261,6 @@ int  v4_node_doing(const v4_node *n);
 void v4_node_done(v4_node *n, v4_cell how);
 void v4_node_have(v4_node *n, unsigned mask);
 
-/* How many words the node has had taken since it last looked at its
- * neighbours (a fetch of either of the two status addresses).  A node that
- * looks before it begins a message (MESH.md 7a) and is blocked writing with
- * this at 0 is blocked on the first word of the message: nothing of it has
- * gone. */
-unsigned v4_node_words_since_look(const v4_node *n);
-
 /* THERE IS NO ONE ON THE PORT the node is blocked at -- writing to it, or
  * reading from that one port -- and there will not be.  A node that can
  * take an error (it has an error register and a fault table: node.h,