Phase 35-39: FAST build optimization complete (+7.13% cumulative)

Phase 35-A: BENCH_MINIMAL gate function elimination (GO +4.39%)
- tiny_front_v3_enabled() → constant true
- tiny_metadata_cache_enabled() → constant 0
- learner_v7_enabled() → constant false
- small_learner_v2_enabled() → constant false

Phase 36: Policy snapshot init-once (GO +0.71%)
- small_policy_v7_snapshot() version check skip in BENCH_MINIMAL
- TLS cache for policy snapshot

Phase 37: Standard TLS cache (NO-GO -0.07%)
- TLS cache for Standard build attempted
- Runtime gate overhead negates benefit

Phase 38: FAST/OBSERVE/Standard workflow established
- make perf_fast, make perf_observe targets
- Scorecard and documentation updates

Phase 39: Hot path gate constantization (GO +1.98%)
- front_gate_unified_enabled() → constant 1
- alloc_dualhot_enabled() → constant 0
- g_bench_fast_front, g_v3_enabled blocks → compile-out
- free_dispatch_stats_enabled() → constant false

Results:
- FAST v3: 56.04M ops/s (47.4% of mimalloc)
- Standard: 53.50M ops/s (45.3% of mimalloc)
- M1 target (50%): 5.5% remaining

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/box/tiny_alloc_gate_box.h

@@ -92,6 +92,8 @@ static inline int tiny_alloc_gate_validate(TinyAllocGateContext* ctx)
         return 0;
     }
     if (ctx->class_idx >= 0 && (uint8_t)ctx->class_idx != meta_cls) {
+        // Phase 34B: Compile-out alloc gate class mismatch counter (default OFF)
+#if HAKMEM_ALLOC_GATE_CLS_MIS_COMPILED
         static _Atomic uint32_t g_alloc_gate_cls_mis = 0;
         uint32_t n = atomic_fetch_add_explicit(&g_alloc_gate_cls_mis, 1, memory_order_relaxed);
         if (n < 8) {
@@ -105,6 +107,9 @@ static inline int tiny_alloc_gate_validate(TinyAllocGateContext* ctx)
                     info.slab_idx);
             fflush(stderr);
         }
+#else
+        (void)0;  // No-op when compiled out
+#endif
         // クラス不一致自体は Fail-Fast せず、ログだけ残す（将来の Guard 差し込みポイント）。
     }