FABRIC-3.10.8 MC-3a: the claim, the physics lock, per-core decision state

VM.running_on claimed by compare-and-swap on switch-in and released once
the context is saved (release_after, sk_vm_switch_finish); a lost claim
returns 1 and the caller re-decides; double claims counted. Per-core
entry_vm and decision_due. g_lock_physics over capsule_vm_physics.c
(rank between switch and registry). KILL refuses a VM running anywhere.
Probe: 15737 claims, 0 lost, 0 double; a core-1 claim of Hera refused.
3-ISA acceptance with a 28-VM churn clean, 0 order violations.

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

include/starkernel/spinlock.h

@@ -50,6 +50,9 @@
  *     g_lock_hermes     kernel-Hermes arena, queues, channels, ledger
  *     g_lock_switch     switch-signal slot table and stamps
  *                       (capsule_vm_switch_signal.c)
+ *     g_lock_physics    fleet physics: node list, heat, touch window, slope
+ *                       (capsule_vm_physics.c, MC-3a); retirement walks
+ *                       the registry under it
  *     g_lock_registry   VM registry list and entries (capsule_birth.c)
  *     g_lock_stadium    Stadium's global part: quota-slot allocation
  *                       (grants) and the shared block table (MC-0d)
@@ -91,6 +94,7 @@ typedef enum sk_lock_rank {
     SK_LOCK_RANK_NONE = 0,     /* unranked: neither checked nor counted */
     SK_LOCK_RANK_HERMES,
     SK_LOCK_RANK_SWITCH,
+    SK_LOCK_RANK_PHYSICS,      /* fleet physics (MC-3a): walks the registry */
     SK_LOCK_RANK_REGISTRY,
     SK_LOCK_RANK_VM_DICT,      /* a VM's dict_lock (sf_mutex_t) */
     SK_LOCK_RANK_VM_TUNING,    /* a VM's tuning_lock (sf_mutex_t) */
@@ -141,6 +145,7 @@ uint64_t sk_lock_order_violations(void);
 extern sk_spinlock_t g_lock_registry;
 extern sk_spinlock_t g_lock_stadium;
 extern sk_spinlock_t g_lock_switch;
+extern sk_spinlock_t g_lock_physics;
 extern sk_spinlock_t g_lock_hermes;
 extern sk_spinlock_t g_lock_doe;
 extern sk_spinlock_t g_lock_log;