fix(v4.0.0): step 6e final review -- texts begun in order; a word no one will read lets its writer go; a cut wire wakes a wait for room; a full console wire is a refusal, not a fault

The final review of step 6e, by a fresh reviewer told to break it, and
what was ruled: fix them all, test first.  Each has a test that failed
before the mend.

- Two texts from one node could be begun in the wrong order when room
  for their answers came between the node's look at the first and at the
  second.  Texts whose answers go by the same port are begun in the order
  they came: (D-MASK), quit.v4.  102 of 700 timings were wrong before.
- A word written with PORT! to a node that speaks whole messages, or to
  a console's port, blocked its writer for ever and cut off every node
  beyond it.  It is error 18 now, whether that node is asleep, running
  or stuck: fabric.c, node.c.
- A node asleep for room on one wire is woken when another of its wires
  is cut.
- A line there was no room for on the lone node's wire was reported as a
  fault and ended the hosted program.  It is Message refused, and the
  prompt comes back: V4_BOOT_LINE_REFUSED.  hosted-check has the case;
  no bare-metal boot has typed it.
- Ruled: text behind held output for the same port is refused though it
  would fit.  MESH.md 7d.4 said otherwise and is corrected.
- The removal test also cuts and re-makes a wire, and has an exchange in
  which output is held at a full wire: 26,814 disturbances in all.
- MESH.md and v4/README.md no longer say that a stuck node holds up no
  other node, that only printing waits, or that no node is left waiting
  on one that is gone; 7d.6 lists the limits and what the products do
  that they did not before.

make -C v4 test and sanitize at both widths, hosted-check, lint.  Three
bare-metal boots: logs/20261013-194827 (amd64), -195131 (aarch64),
-195518 (riscv64).  POST 538 of 538, word_count=317,
dict_hash=0xe5a57f3eb72ff94a on all six; 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.

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

v4/tests/host_map.h

@@ -90,6 +90,7 @@
 #define S_ON         (BUF0_W - 38)              /*   and whether its mark has been put at its first message */
 #define KEEP         (BUF0_W - 40)              /* the port the answer to the text being done goes by, on whose wire 8 cells are kept for it; -1: none */
 #define DEFER        (BUF0_W - 41)              /* a port whose wire had no room for the answer to text that waits to be begun; -1: none */
+#define D_MASK       (BUF0_W - 8)               /*   and a bit for each such port: text whose answer goes by one is not begun on this pass */
 #define IN_HDR       (BUF0_W - 56)              /* the seven words of the message a wire's mark is at */
 #define ONE          (BUF0_W - 49)              /* the one word of text of a NACK, a GONE or an answer, coming or going */
 #define OUT_HDR      (BUF0_W - 112)             /* the seven words of a message this node is putting on a wire */
@@ -104,7 +105,7 @@
 #define SEND_PTR     (BUF0_W - 101)             /* where the next word of a text being made ready to send goes */
 #define OUT_TEXT     (OUT_W - 64)               /* what was printed, four characters to a cell, as it goes on the wire: 64 cells */
 #define SEND_TEXT    (OUT_W - 400)              /* the text of a message SEND is putting, four characters to a cell: 256 cells */
-/* FREE, plain memory: BUF0_W - 8; - 32 .. - 21; - 122 .. - 113; BUF0_W - 144 .. - 141 (what a flush makes zero after
+/* FREE, plain memory: BUF0_W - 32 .. - 21; - 122 .. - 113; BUF0_W - 144 .. - 141 (what a flush makes zero after
  * a full output buffer); and OUT_W - 144 .. OUT_W - 65.  They and
  * the cells above held the messages waiting, the refusals owed and what went with them (MESH.md 7a, 7b), which a
  * node no longer keeps. */
@@ -227,6 +228,7 @@ static int host_load(v4_text *tx, v4_node *n, const char *const *files, unsigned
     v4_text_constant(tx, "(S-ON)", S_ON);
     v4_text_constant(tx, "(KEEP)", KEEP);
     v4_text_constant(tx, "(DEFER)", DEFER);
+    v4_text_constant(tx, "(D-MASK)", D_MASK);
     v4_text_constant(tx, "(IN)", IN_HDR);
     v4_text_constant(tx, "(ONE)", ONE);
     v4_text_constant(tx, "(OUT-HDR)", OUT_HDR);