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/src/fabric.c

@@ -25,7 +25,6 @@ void v4_fabric_init(v4_fabric *f, v4_place *places, unsigned capacity)
     f->queue_free = 0;
     f->queue_first = 0;
     f->gone_error = 0;
-    f->interrupt_error = 0;
     for (i = 0; i < capacity; i++) clear_place(&places[i]);
 }
 
@@ -34,11 +33,6 @@ void v4_fabric_gone_error(v4_fabric *f, v4_cell code)
     f->gone_error = code;
 }
 
-void v4_fabric_interrupt_error(v4_fabric *f, v4_cell code)
-{
-    f->interrupt_error = code;
-}
-
 void v4_fabric_grow(v4_fabric *f, v4_place *places, unsigned capacity)
 {
     unsigned i;
@@ -463,24 +457,6 @@ unsigned v4_fabric_step(v4_fabric *f)
     for (i = 0; i < f->capacity; i++)
         if (awake(f, i) && f->place[i].node->n.reading && !f->place[i].node->n.given) done += hand_over_read(f, i);
 
-    /* a node blocked on the first word of a message to a node that is not
-     * reading, while a device of its own has something for it */
-    if (f->interrupt_error != 0)
-        for (i = 0; i < f->capacity; i++) {
-            v4_node *n;
-            unsigned k;
-            if (!awake(f, i)) continue;
-            n = &f->place[i].node->n;
-            if (!n->asking || f->place[i].wire[n->ask_port].kind != V4_WIRE_NODE || v4_node_words_since_look(n) != 0) continue;
-            for (k = 0; k < V4_PORTS; k++) {
-                const v4_wire *w = &f->place[i].wire[k];
-                if (w->kind == V4_WIRE_DEVICE && w->device->pending && w->device->pending(w->device->self)) {
-                    done += (unsigned)v4_node_port_gone(n, f->interrupt_error);
-                    break;
-                }
-            }
-        }
-
     /* a node blocked at one port that nothing is wired to */
     if (f->gone_error != 0)
         for (i = 0; i < f->capacity; i++) {

v4/src/node.c

@@ -124,8 +124,8 @@ v4_cell v4_node_fetch(v4_node *n, v4_cell addr)
     {
         int port = v4_node_port_index(n, addr);
         if (port == (int)V4_PORTS + 1) return (v4_cell)n->last_from;
-        if (port == (int)V4_PORTS + 2) { n->since_look = 0; return (v4_cell)n->writers; }
-        if (port == (int)V4_PORTS + 3) { n->since_look = 0; return (v4_cell)n->readers; }
+        if (port == (int)V4_PORTS + 2) return (v4_cell)n->writers;
+        if (port == (int)V4_PORTS + 3) return (v4_cell)n->readers;
         if (port == (int)V4_PORT_WIRE) return (v4_cell)n->wire;
         if (port == (int)V4_PORT_A) return n->wire_a;
         if (port == (int)V4_PORT_B) return n->wire_b;
@@ -189,7 +189,6 @@ void v4_node_port_attach(v4_node *n, v4_cell base)
     n->last_from = 0;
     n->writers = 0;
     n->readers = 0;
-    n->since_look = 0;
     n->wire = 0;
     n->wire_a = 0;
     n->wire_b = 0;
@@ -240,7 +239,6 @@ void v4_node_born(v4_node *n, v4_cell base)
 void v4_node_port_served(v4_node *n)
 {
     n->asking = 0;
-    n->since_look++;
 }
 
 int v4_node_doing(const v4_node *n)
@@ -259,11 +257,6 @@ void v4_node_have(v4_node *n, unsigned mask)
     n->have = mask;
 }
 
-unsigned v4_node_words_since_look(const v4_node *n)
-{
-    return n->since_look;
-}
-
 int v4_node_port_gone(v4_node *n, v4_cell code)
 {
     if (code == 0 || n->error_reg < 0 || n->fault_vector < 0 || n->stopped) return 0;