fix(v4.0.0): a waiting node goes on passing on and paying; KILL is not held by a stuck node

Found in the five-node test, each with a check that failed first:
- A node with answers it could not give to two stuck senders began no
  text at all.  It now holds back only text from a sender whose own
  answer is still with it.
- KILL waited to tell a stuck node, and a typed line that broke it left
  the nodes after it untold.  GONE is put with the messages waiting, as
  how text ended is, and goes when it can.
- So that 'tell, then wait' still works, AWAIT does what (IDLE) does but
  for beginning text: it looks through the messages waiting, offers what
  is to be passed on and what is owed, and sleeps in the wait.  A waiting
  node no longer keeps back what passes through it.
- A node in the wait with an offer on a port that turns out to have
  nothing on it is woken and told so (which port: 2 * V4_PORTS + k); no
  error is raised on it.  (GATE) makes it error 18; (IDLE) and AWAIT let
  the message go.  Before, removing a node raised 'No one on that port'
  on the unrelated text of a neighbour that had something queued for it.

make -C v4 test and sanitize at both widths, hosted-check.

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

v4/src/fabric.c

@@ -269,7 +269,7 @@ unsigned v4_fabric_step(v4_fabric *f)
             else if (v4_node_in_wait(n)) {                    /* an offer on a port with nothing on it */
                 unsigned k;
                 for (k = 0; k < V4_PORTS; k++)
-                    if ((n->offers & (1u << k)) && f->place[i].wire[k].kind == V4_WIRE_NONE) { done += (unsigned)v4_node_port_gone(n, f->gone_error); break; }
+                    if ((n->offers & (1u << k)) && f->place[i].wire[k].kind == V4_WIRE_NONE) { done += (unsigned)v4_node_offer_gone(n, k); break; }
             }
         }