Stage MC-0c: shared VM code made per-VM or atomic (FABRIC-3.10.8 §3.4)

- Dictionary lookup index is per VM (vm->fc_index, struct SfFcIndex):
  was one global index rebuilt whenever a different VM was searched, and
  heat reorganization could reorder another VM's buckets. Allocated on
  first lookup, freed by vm_cleanup(); allocation failure counted/logged,
  lookup falls back to a newest-first dictionary walk.
- PRNG: still one stream, stepped by compare-and-swap; SEED one store.
- state_variable removed (write-only; STATE is vm->mode).
- Sweep additions (Captain Bob's ruling): heartbeat_export.c delta
  last-values moved into each VM's HeartbeatState (were statics shared by
  every VM -- wrong across VMs today); TOP-WORDS list heap-sized per call
  (was static [1000]); inference_outputs_to_string() takes a caller
  buffer; three failure counters atomic; crc64 table published with
  release/acquire.
- Confirmed, unchanged: g_runtime compiled out of the kernel,
  g_hotwords_cache unreferenced, ttf cache core-0-only.
- Probe (removed): every VM has its own index; two VMs searched
  alternately 2x5000 lookups: 0 rebuilds, 0 wrong-VM results, all three
  ISAs.
- Standard sequence on amd64/aarch64/riscv64: dict_hash set unchanged,
  G byte-identical, MINT/WIREBIND/USE ok, conservation true, 0 idle growth.

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

src/physics_pipelining_metrics.c

@@ -212,7 +212,7 @@ int transition_metrics_init(WordTransitionMetrics *metrics) {
  */
 static uint64_t g_transition_grow_failures;
 
-uint64_t transition_metrics_grow_failures(void) { return g_transition_grow_failures; }
+uint64_t transition_metrics_grow_failures(void) { return __atomic_load_n(&g_transition_grow_failures, __ATOMIC_RELAXED); }
 
 int transition_metrics_record(WordTransitionMetrics *metrics, uint32_t next_word_id, uint32_t dict_size) {
     if (!metrics || next_word_id >= dict_size) {
@@ -234,7 +234,7 @@ int transition_metrics_record(WordTransitionMetrics *metrics, uint32_t next_word
         }
         grown = (uint64_t *)calloc(new_cap, sizeof(uint64_t));
         if (!grown) {
-            g_transition_grow_failures++;
+            __atomic_add_fetch(&g_transition_grow_failures, 1, __ATOMIC_RELAXED); /* MC-0c: any core */
             log_message(LOG_ERROR, "transition_heat can't grow: dropped");
             return -1;
         }