Phase 3 C3: Static Routing A/B Test ADOPT (+2.20% Mixed gain)

Step 2 & 3 Complete:
- A/B test (Mixed 10-run): STATIC_ROUTE=0 (38.91M) → =1 (39.77M) = +2.20% avg
  - Median gain: +1.98%
  - Result: ✅ GO (exceeds +1.0% threshold)

- Decision: ✅ ADOPT into MIXED_TINYV3_C7_SAFE preset
  - bench_profile.h line 77: HAKMEM_TINY_STATIC_ROUTE=1 default
  - Learner auto-disables static route when HAKMEM_SMALL_LEARNER_V7_ENABLED=1

Implementation Summary:
- core/box/tiny_static_route_box.{h,c}: Research box (Step 1A)
- core/front/malloc_tiny_fast.h: Route lookup integration (Step 1B, lines 249-256)
- core/bench_profile.h: Bench sync + preset adoption

Cumulative Phase 2-3 Gains:
- B3 (Routing shape): +2.89%
- B4 (Wrapper split): +1.47%
- C3 (Static routing): +2.20%
- Total: ~6.8% (35.2M → ~39.8M ops/s)

Next: Phase 3 C1 (TLS Prefetch, expected +2-4%)

🤖 Generated with Claude Code

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

core/box/tiny_header_box.h

@@ -35,7 +35,7 @@
 // All code must use this instead of hardcoded class_idx checks.
 //
 // Implementation:
-//   - Delegates to tiny_user_offset() from tiny_layout_box.h
+//   - Delegates to tiny_nextptr_offset() from tiny_layout_box.h
 //   - offset=0 → header overwritten by next pointer → false
 //   - offset!=0 → header preserved → true
 //
@@ -46,9 +46,9 @@
 static inline bool tiny_class_preserves_header(int class_idx) {
 #if HAKMEM_TINY_HEADER_CLASSIDX
     // Delegate to tiny_layout_box.h specification (Single Source of Truth)
-    // user_offset=0 → header overwritten (C0, C7)
-    // user_offset=1 → header preserved (C1-C6)
-    return tiny_user_offset(class_idx) != 0;
+    // next_off=0 → header overwritten (C0, C7)
+    // next_off=1 → header preserved (C1-C6)
+    return tiny_nextptr_offset(class_idx) != 0;
 #else
     // Headers disabled globally
     (void)class_idx;