feat(v4): the mesh boot to spec -- Hera born empty in the kernel's fabric; births, kills, every node stepping together (#189)

ENGINE step 4 Phase 1, Tasks 5b-5d, and the edge cases (Captain Bob, 2026-11-13: "Build it to proper
spec"; "Check for the edge cases"; "Yes, add it to v4-checks").

- v4/system/mesh.c, v4/include/v4/mesh.h: the nucleus assembled by the ROM and given to Hera as F18
  cells; Hera born empty at place 0, the kernel on port 0, the console on port 1; told she is 10, in the
  registry, the kernel's words, FORTH-79, sealed, POST, the kernel's capsules. NODE-BORN / NODE-KILL in
  the owner's room.
- No scheduler: v4_mesh_tell returns once the node told says how its text ended, and
  v4_mesh_step / v4_mesh_busy let the host step the fabric while it waits, so nodes run between
  lines as during them. A text left "waiting" is owed its end: the next line ends it "Interrupted"
  and is then run (MESH.md 7b.6).
- kernel: sk_v4.c boots through the mesh; its idle steps the fabric while a node can run, and halts
  only when none can (#151 kept). stadium_return_quota and stadium_ops_forget on a kill.
- Tests: v4/tests/test_mesh_boot.c (32 checks: the boot, births, kills, rebirth, a live number, a
  fault, no such node, Hera not killing herself, no room, a line too long, a node running for ever,
  a wait broken by the next line), run by `make -C v4 test` and under ASan+UBSan by `sanitize`
  (v4-checks); kernel/tests quota return; scripts/qemu_session.py births() and the edges on bare
  metal.
- Docs: ENGINE.md 6 "who runs next" struck (settled: no scheduler); the Phase 1 plan; FABRIC-3
  XLVIII.23; .claude/memory/rules.md: alpha.5 closed to new work.
- Evidence: v4-checks 80 programs under the sanitizers, 0 failures; the hosted builds alike; two
  stopped v4-checks runs labelled STOPPED; three development amd64 boots labelled.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm

v4/system/boot.c

@@ -568,19 +568,41 @@ static int load_system(const v4_boot *b)
 
 /* ---- the whole boot ------------------------------------------------------ */
 
-int v4_boot_run(const v4_boot *b)
-{
-    unsigned i;
+/* ---- what the mesh boot shares (v4/mesh.h; #189) ---------------------------- */
 
+int v4_boot_assemble(const v4_boot *b)
+{
     /* a node is born with nothing in it, and its ROM assembles the system */
     if (!v4_image_born(b->n, b->es, b->h, b->im)) {
-        say(b, "V4: the memory map is not for this build of the engine\nPARITY:FAIL\nPOST: FAILED\n");
+        say(b, "V4: the memory map is not for this build of the engine\n");
         return 0;
     }
     /* its console's wire, with nothing on it */
     v4_wire_reset(TO_NODE); v4_wire_reset(FROM_NODE);
     v4_blocks_init(&boot_blocks, b->im->block_window);
-    if (!load_system(b)) { say(b, "PARITY:FAIL\nPOST: FAILED\n"); return 0; }
+    return load_system(b);
+}
+
+uint32_t v4_boot_word_count(const v4_node *n, const v4_image *im) { return word_count(n, im); }
+void v4_boot_say_dec(const v4_boot *b, uint32_t v) { say_dec(b, v); }
+void v4_boot_say_hex(const v4_boot *b, uint64_t v) { say_hex(b, v); }
+
+const uint8_t *v4_boot_capsule(const v4_boot *b, const char *name, uint32_t *length, uint64_t *id, uint64_t *hash)
+{
+    const CapsuleDesc *cap;
+    const uint8_t *p = open_capsule(b, name, &cap);
+    if (!p) return 0;
+    *length = (uint32_t)cap->length;
+    *id = cap->capsule_id;
+    *hash = cap->content_hash;
+    return p;
+}
+
+int v4_boot_run(const v4_boot *b)
+{
+    unsigned i;
+
+    if (!v4_boot_assemble(b)) { say(b, "PARITY:FAIL\nPOST: FAILED\n"); return 0; }
 
     /* the kernel's words, before any capsule that might use one */
     for (i = 0; i < b->word_count; i++) {