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>

include/inference_engine.h

@@ -210,9 +210,12 @@ void inference_engine_run(InferenceInputs *inputs, InferenceOutputs *outputs);
  * Format: "window_width=XXX variance_q48=YYYY slope_q48=ZZZZ fit_quality=WWWW"
  *
  * @param outputs Inference outputs struct
- * @return Pointer to static string (valid until next call)
+ * @param buf     Caller's buffer (256 bytes holds any output) -- FABRIC-3.10.8
+ *                MC-0c: no longer a static buffer shared by every VM
+ * @param cap     Size of @p buf
+ * @return @p buf
  */
-const char* inference_outputs_to_string(const InferenceOutputs *outputs);
+const char* inference_outputs_to_string(const InferenceOutputs *outputs, char *buf, size_t cap);
 
 /*
  * @brief Validate inference outputs for sanity