Stage S-1b: dictionary word ids grow with the dictionary; a word that can't get an id is refused whole (FABRIC-3.9.0 §8.1)

- word_id_map / recycled_word_ids are heap tables (one shared capacity,
  64 doubling), grown all-or-nothing by allocate-copy-free. Numbering is
  unchanged, so boot parity is unchanged.
- vm_create_word() takes the id before linking; on failure it frees the
  entry, sets vm->error, logs LOG_ERROR and counts
  (vm_dictionary_word_id_refusals()). No word runs with WORD_ID_INVALID.
- Readers of the id space bound by vm->next_word_id, not DICTIONARY_SIZE.
- transition_heat gets its own capacity and grows on record (was sized
  once -- a heap overflow under a dynamic bound); every reader bounds by it.
- Stadium id->cell rows start empty and grow on dispatch; a failed grow is
  logged, counted and not admitted. S-2 (the cell pool) stays open.

Probe (reverted), identical on amd64/aarch64/riscv64: +2000 words get real
ids (capacity 4096); a word at id 2738 lands 200x in the rolling window and
is Stadium-admitted; FORGET recycles across the old boundary; an injected
grow failure refuses the word whole (NULL, error, counter, dictionary
unchanged) and the retry succeeds. 3-ISA acceptance passes; boot parity
(531, 0x572daac83b797332) and the dict_hash set unchanged.

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

include/physics_pipelining_metrics.h

@@ -154,11 +154,15 @@ typedef struct WordTransitionMetrics {
      * transition_heat[i]: Number of times word with index i has been
      *                     executed immediately after this word.
      *
-     * Dynamically allocated array of size DICTIONARY_SIZE.
+     * Dynamically allocated, transition_heat_cap entries long.
      * Initialized to NULL; allocated on first use to save memory
-     * for words that are never executed.
+     * for words that are never executed, and grown when a word id at or
+     * past transition_heat_cap is recorded (Stage S-1b: word ids are no
+     * longer capped at DICTIONARY_SIZE, so no fixed length can hold them).
+     * Every reader bounds by transition_heat_cap, never by a global size.
      */
     uint64_t *transition_heat;
+    uint32_t transition_heat_cap;
 
     /** Total number of transitions observed from this word */
     uint64_t total_transitions;
@@ -264,11 +268,14 @@ int transition_metrics_init(WordTransitionMetrics *metrics);
  *
  * @param metrics Metrics for the current word
  * @param next_word_id Index of word that executed next
- * @param dict_size Total number of words in dictionary (for array bounds)
- * @return 0 on success, -1 on invalid word_id
+ * @param dict_size The VM's word-id bound (vm->next_word_id): every issued id is below it
+ * @return 0 on success, -1 on invalid word_id or a failed grow (logged, counted)
  */
 int transition_metrics_record(WordTransitionMetrics *metrics, uint32_t next_word_id, uint32_t dict_size);
 
+/* S-1b: transitions dropped because a transition_heat array couldn't grow. */
+uint64_t transition_metrics_grow_failures(void);
+
 /*
  * Get the probability (Q48.16 format) of a specific word following this word.
  *