Stage 3 follow-on: message-arrival eligibility hook + trampoline-blind switch-storm fix (FABRIC-3.md §XXVIII.2)

Implements the message-arrival eligibility signal FABRIC-3.md §XXVIII.1 left
open (has_work per-slot flag, set via new SWITCH-MARK-WORK primitive from
MSG-SEND) so an idle VM never becomes a switch target purely by waiting out
the readiness threshold.

Also root-causes and fixes a second, independent switch-storm: the tick's
"who is current" check used vm_log_attributed_vm(), which can't see a VM
parked in switch.c's own raw trampoline. Replaced with a dedicated
g_switch_current_vm tracked by the switch mechanism itself, and moved
target-slot eligibility reset to the switch decision point instead of
relying on ISR polling to observe a window that can be only a few
instructions wide.

Verified live on all 3 architectures: clean boot to zuse@Hera] ok>, live
cross-VM message dispatch, and (since a quiet log looks identical to a
livelocked storm once the DoE probe is gone) confirmed genuine REPL
liveness via QMP send-key + screendump on aarch64/riscv64, not log
inspection alone.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BWpNjdwPtFLuVLaAq44L9K

src/starkernel/kernel_main.c

@@ -64,6 +64,7 @@ EFI_RUNTIME_SERVICES *g_sk_runtime_services = NULL;
 #include "starkernel/capsule_birth.h"  /* capsule_birth_mama, capsule_find_mama_init */
 #include "starkernel/capsule_zuse_boot.h" /* capsule_zuse_boot_load_root_pubkey */
 #include "starkernel/capsule_vm_switch_signal.h" /* FABRIC-3.md §XXVIII Stage 3 */
+#include "starkernel/vm/switch.h" /* sk_vm_switch_set_current() -- Stage 3 follow-on */
 #include "starkernel/artemis_sig.h" /* artemis_sig_check/genesis_stamp */
 #include "starkernel/kmalloc.h"
 #include "starkernel/repl.h"
@@ -997,6 +998,11 @@ static void kernel_main_deep(BootInfo *boot_info) {
         VMRegistryEntry hera_entry, hermes_entry, artemis_entry;
         if (capsule_vm_registry_get(vm_uuid_hera(), &hera_entry) == 0) {
             sk_vm_switch_signal_register(hera_entry.vm_id);
+            /* Seed the switch mechanism's own "who is running" tracker
+             * (FABRIC-3.md §XXVIII Stage 3 follow-on, 2026-09-14) -- Hera
+             * is genuinely the one running here, before any switch has
+             * ever happened. */
+            sk_vm_switch_set_current(mama);
         }
         if (capsule_vm_find_by_name_nocase("Hermes", &hermes_entry) == 0 &&
             hermes_entry.state == VM_STATE_LIVE) {