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/free_dispatch_stats_box.h

@@ -1,6 +1,7 @@
 #ifndef HAKMEM_FREE_DISPATCH_STATS_BOX_H
 #define HAKMEM_FREE_DISPATCH_STATS_BOX_H
 
+#include "../hakmem_build_flags.h"  // Phase 39: HAKMEM_BENCH_MINIMAL (GO +1.98%)
 #include <stdint.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -26,13 +27,18 @@ typedef struct FreeDispatchStats {
 } FreeDispatchStats;
 
 // ENV gate
+// Phase 39: BENCH_MINIMAL → 固定 false (GO +1.98%)
 static inline bool free_dispatch_stats_enabled(void) {
+#if HAKMEM_BENCH_MINIMAL
+    return false;  // FAST v3: 定数化 (stats OFF)
+#else
     static int g_enabled = -1;
     if (__builtin_expect(g_enabled == -1, 0)) {
         const char* e = getenv("HAKMEM_FREE_DISPATCH_STATS");
         g_enabled = (e && *e && *e != '0') ? 1 : 0;
     }
     return g_enabled;
+#endif
 }
 
 // Global stats instance