feat(v4): a believed GONE is handed to the word in (GONE-HOOK) (MESH.md 9a)

COLD takes out a hook it forgets.  The system changed, so dict_hash did:
hosted, all three ISAs, word_count=318 dict_hash=0x1b5c633fd6bdd143.

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

v4/tests/host_map.h

@@ -119,7 +119,7 @@
 /* THE IMAGE RECORD: where the system's source says, with `store`, the addresses a host needs (v4/image.h): where the
  * node waits for a message, its fault table, and KEY's code. */
 #define ROM_IMG      (BUF0_W - 119)             /* idle, fault table, KEY, the word after KEY: 4 cells */
-/* FREE, plain memory: BUF0_W - 22 .. - 21; - 115 .. - 113; BUF0_W - 144 .. - 141 (what a flush makes zero after
+/* FREE, plain memory: BUF0_W - 22; - 115 .. - 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. */
@@ -205,6 +205,7 @@ enum { V4_ROM_ERRORS(ROM_ERR_ENUM_) ROM_ERR_END_ };
 #define ROM_ADDR_TOP      ((v4_cell)(V4_NODE_WORDS + V4_ROM_WORDS - 1u))   /* the top of the address space */
 #define WORD_DEFINED   (BUF0_W - 11)             /* the xt of the word that is told of each new entry, or 0 */
 #define WORD_FORGOTTEN (BUF0_W - 12)             /* the xt of the word that is told when entries go, or 0 */
+#define GONE_HOOK      (BUF0_W - 21)             /* the xt of the word a believed GONE is handed to, or 0 (MESH.md 9a.2, ruling 7) */
 #define LOG_LEVEL    (BUF0_W - 5)               /* the level at or below which a message is printed */
 #define BOOT_CELLS   (BVARS + 14)               /* (BOOT): DP and LATEST as the loader left them, 2 cells */
 #define BUF0_W       (BVARS - (v4_cell)(V4_BLOCK_SLOTS * V4_BLOCK_CELLS))   /* the block window: the kernel's slots, 256 cells each (v4/blocks.h) */
@@ -330,6 +331,7 @@ static unsigned host_branch_slots(void)
     X("(OUT)", OUT_W) \
     X("(WORD-DEFINED)", WORD_DEFINED) \
     X("(WORD-FORGOTTEN)", WORD_FORGOTTEN) \
+    X("(GONE-HOOK)", GONE_HOOK) \
     X("BLOCK#", V4_REQ_BLOCK)               /* the kernel's block requests (v4/blocks.h) */ \
     X("BUFFER#", V4_REQ_BUFFER) \
     X("UPDATE#", V4_REQ_UPDATE) \

v4/tests/test_host_mesh.c

@@ -1096,6 +1096,26 @@ int main(void)
         CHECK(undone == 0 && wrong == 0, "whenever the room came, both texts were done, the first first: %u not done, %u in the wrong order, the first when it came at step %u", undone, wrong, first_wrong);
     }
 
+    /* ---- A BELIEVED GONE IS HANDED ON (MESH.md 9a.2, ruling 7; 9a.3) ----
+     * The word in (GONE-HOOK) is given the number of the node that is gone, each time a GONE is believed:
+     * centre.4th puts GONE-DOWN there, which tells the nodes the node birthed.  Here node 11 has a word that
+     * tells node 12; node 12 believes it, since node 11 is its centre, and forgets its way to 44. */
+    CHECK(row() && told(12, "44 2 ROUTE") && told(11, "44 3 ROUTE"), "a row; nodes 11 and 12 each know a way to 44");
+    {
+        v4_cell ways11 = pool[mid].n.mem[ROUTE_COUNT], ways12 = pool[far].n.mem[ROUTE_COUNT];
+        CHECK(told(10, "44 11 GONE") && pool[mid].n.mem[ROUTE_COUNT] == ways11 - 1 && pool[far].n.mem[ROUTE_COUNT] == ways12 && asleep(far),
+              "with nothing in (GONE-HOOK) node 11 believes a GONE from its centre and tells no one");
+        CHECK(told(11, "44 3 ROUTE  : DOWN 12 GONE ;  ' DOWN (GONE-HOOK) !"), "node 11 is given a word to hand a GONE on with");
+        CHECK(told(10, "44 11 GONE") && pool[mid].n.mem[ROUTE_COUNT] == ways11 - 1 && pool[far].n.mem[ROUTE_COUNT] == ways12 - 1 && asleep(far) && asleep(mid),
+              "now node 11 believes it and hands it on: node 12 believes it from its centre and forgets 44 too");
+        CHECK(told(12, "44 2 ROUTE") && told(11, "44 3 ROUTE") && told(12, "44 12 GONE") && pool[mid].n.mem[ROUTE_COUNT] == ways11,
+              "a GONE that is not believed -- node 12 is not node 11's centre -- is not handed on");
+        CHECK(v4_fabric_wire_kernel(&f, mid, 0, &kernel_dev), "a kernel on node 11's port 0, for COLD's EMPTY-BUFFERS");
+        CHECK(strstr(tell(11, "COLD"), "Cold Start") != NULL && strcmp(tell(11, "(GONE-HOOK) @ ."), "0 ") == 0,
+              "COLD forgets DOWN, so (GONE-HOOK) no longer points at it: \"%s\"", printed);
+        CHECK(strcmp(tell(10, "1 2 + ."), "3 ") == 0 && strcmp(tell(11, "1 2 + ."), "3 ") == 0 && strcmp(tell(12, "1 2 + ."), "3 ") == 0, "and every node answers");
+    }
+
     /* ---- A NODE REMOVED, OR A WIRE CUT, AT EVERY STEP (MESH.md 7d.7, acceptance 6) ----
      * Three exchanges, each played once whole and then once for every step it takes with node 11 removed at
      * that step, again with node 12 removed, and again with the wire between them cut and made again: the