Stage E: every born VM is a switch participant (FABRIC-3.8 §3.6, G4)

capsule_birth_baby() registers each VM at its LIVE completion point, beside
the common-channel subscription. register() is idempotent. The Artemis/
Hestia registrations in kernel_main.c and WIREBIND's own call are removed
(Hera, never born through capsule_birth_baby, stays with set_current).

Probe (restored away): Tripod registered once each (3 slots), a
WORKER-BIRTH VM becomes a participant with no hand registration (4) and
KILL frees it (3), WIREBIND registers exactly console+user, zero
duplicates, on amd64/aarch64/riscv64. Acceptance: dict_hash unchanged,
relay 3, idle growth 0.

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

src/starkernel/capsule/capsule_birth.c

@@ -920,6 +920,20 @@ CapsuleRunResult capsule_birth_baby(
      * and does not fail the birth itself. */
     (void)sk_hermes_channel_subscribe(SK_HERMES_CHANNEL_COMMON, vm_id);
 
+    /* FABRIC-3.8.md §3.6 (Stage E, G4): every born VM is a switch
+     * participant -- same choke point, same "only once birth has fully
+     * completed" rule as the subscription above (its capsule code has
+     * already run to completion on the birthing VM's stack). BIRTH,
+     * WORKER-BIRTH, UNATTENDED-BIRTH and WIREBIND identities all pass
+     * through here, so none of them registers on its own any more. Soft
+     * failure, same posture: a full table leaves this VM runnable only by
+     * VM-EXEC, not a failed birth. A VM with no native stack is registered
+     * but never chosen (sk_vm_switch_decide() skips it). */
+    if (sk_vm_switch_signal_register(vm_id) < 0) {
+        log_message(LOG_WARN, "capsule_birth_baby: switch-signal table full -- %s won't be switched to",
+                    capsule_name);
+    }
+
     capsule_parity_log_birth(vm_id, cap->capsule_id, cap->content_hash, dict_hash);
 
     /* §H.12 step 11: applied AFTER dict_hash/parity logging above, not