Phase 36-37: TinyHotHeap v2 HotBox redesign and C7 current_page policy fixes

- Redefine TinyHotHeap v2 as per-thread Hot Box with clear boundaries
- Add comprehensive OS statistics tracking for SS allocations
- Implement route-based free handling for TinyHeap v2
- Add C6/C7 debugging and statistics improvements
- Update documentation with implementation guidelines and analysis
- Add new box headers for stats, routing, and front-end management

core/box/tiny_front_stats_box.h

@@ -0,0 +1,42 @@
+// tiny_front_stats_box.h - Front class distribution counters (ENV gated)
+#pragma once
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdatomic.h>
+#include "../hakmem_tiny_config.h"
+
+extern _Atomic uint64_t g_tiny_front_alloc_class[TINY_NUM_CLASSES];
+extern _Atomic uint64_t g_tiny_front_free_class[TINY_NUM_CLASSES];
+
+static inline int tiny_front_class_stats_enabled(void) {
+    static int g = -1;
+    if (__builtin_expect(g == -1, 0)) {
+        const char* e = getenv("HAKMEM_TINY_FRONT_CLASS_STATS");
+        g = (e && *e && *e != '0') ? 1 : 0;
+    }
+    return g;
+}
+
+static inline int tiny_front_class_stats_dump_enabled(void) {
+    static int g = -1;
+    if (__builtin_expect(g == -1, 0)) {
+        const char* e = getenv("HAKMEM_TINY_FRONT_CLASS_STATS_DUMP");
+        const char* e2 = getenv("HAKMEM_TINY_FRONT_CLASS_STATS");
+        g = ((e && *e && *e != '0') || (e2 && *e2 && *e2 != '0')) ? 1 : 0;
+    }
+    return g;
+}
+
+static inline void tiny_front_alloc_stat_inc(int class_idx) {
+    if (__builtin_expect(tiny_front_class_stats_enabled(), 0)) {
+        atomic_fetch_add_explicit(&g_tiny_front_alloc_class[class_idx], 1, memory_order_relaxed);
+    }
+}
+
+static inline void tiny_front_free_stat_inc(int class_idx) {
+    if (__builtin_expect(tiny_front_class_stats_enabled(), 0)) {
+        atomic_fetch_add_explicit(&g_tiny_front_free_class[class_idx], 1, memory_order_relaxed);
+    }
+}
+