Phase 4 E3-4: ENV Constructor Init (+4.75% GO)

Target: Eliminate E1 lazy init check overhead (3.22% self%)
- E1 consolidated ENV gates but lazy check remained in hot path
- Strategy: __attribute__((constructor(101))) for pre-main init

Implementation:
- ENV gate: HAKMEM_ENV_SNAPSHOT_CTOR=0/1 (default 0, research box)
- core/box/hakmem_env_snapshot_box.c: Constructor function added
  - Reads ENV before main() when CTOR=1
  - Refresh also syncs gate state for bench_profile putenv
- core/box/hakmem_env_snapshot_box.h: Dual-mode enabled check
  - CTOR=1 fast path: direct global read (no lazy branch)
  - CTOR=0 fallback: legacy lazy init (rollback safe)
  - Branch hints adjusted for default OFF baseline

A/B Test Results (Mixed, 10-run, 20M iters, E1=1):
- Baseline (CTOR=0): 44.28M ops/s (mean), 44.60M ops/s (median)
- Optimized (CTOR=1): 46.38M ops/s (mean), 46.53M ops/s (median)
- Improvement: +4.75% mean, +4.35% median

Decision: GO (+4.75% >> +0.5% threshold)
- Expected +0.5-1.5%, achieved +4.75%
- Lazy init branch overhead was larger than expected
- Action: Keep as research box (default OFF), evaluate promotion

Phase 4 Cumulative:
- E1 (ENV Snapshot): +3.92%
- E2 (Alloc Per-Class): -0.21% (NEUTRAL, frozen)
- E3-4 (Constructor Init): +4.75%
- Total Phase 4: ~+8.5%

Deliverables:
- docs/analysis/PHASE4_E3_ENV_CONSTRUCTOR_INIT_DESIGN.md
- docs/analysis/PHASE4_E3_ENV_CONSTRUCTOR_INIT_NEXT_INSTRUCTIONS.md
- docs/analysis/PHASE4_COMPREHENSIVE_STATUS_ANALYSIS.md
- docs/analysis/PHASE4_EXECUTIVE_SUMMARY.md
- scripts/verify_health_profiles.sh (sanity check script)
- CURRENT_TASK.md (E3-4 complete, next instructions)

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

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

core/box/hakmem_env_snapshot_box.h

@@ -10,10 +10,16 @@
 //   - Lazy init with version-based refresh (follows tiny_front_v3_snapshot pattern)
 //   - Learner interlock: tiny_metadata_cache_eff = cache && !learner
 //
+// E3-4 Extension: Constructor init to eliminate lazy check overhead
+//   - ENV: HAKMEM_ENV_SNAPSHOT_CTOR=0/1 (default 0)
+//   - When =1: Gate init runs in constructor (before main)
+//   - Eliminates 3.22% lazy init check overhead
+//
 // Benefits:
 //   - 3 TLS reads → 1 TLS read (66% reduction)
 //   - 3 lazy init checks → 1 lazy init check
-//   - Expected gain: +1-3% (conservative from 3.26% overhead)
+//   - E3-4: Lazy init check → no check (constructor init)
+//   - Expected gain: +1-3% (E1) + +0.5-1.5% (E3-4)
 
 #ifndef HAK_ENV_SNAPSHOT_BOX_H
 #define HAK_ENV_SNAPSHOT_BOX_H
@@ -47,18 +53,29 @@ static inline const HakmemEnvSnapshot* hakmem_env_snapshot(void) {
     return &g_hakmem_env_snapshot;
 }
 
+// E3-4: Global gate state (defined in hakmem_env_snapshot_box.c)
+extern int g_hakmem_env_snapshot_gate;
+extern int g_hakmem_env_snapshot_ctor_mode;
+
 // ENV gate: default OFF (research box, set =1 to enable)
+// E3-4: Dual-mode - constructor init (fast) or legacy lazy init (fallback)
 static inline bool hakmem_env_snapshot_enabled(void) {
-    static int g = -1;
-    if (__builtin_expect(g == -1, 0)) {
+    // E3-4 Fast path: constructor mode (no lazy check, just global read)
+    // Default is OFF, so ctor_mode==1 is UNLIKELY.
+    if (__builtin_expect(g_hakmem_env_snapshot_ctor_mode == 1, 0)) {
+        return g_hakmem_env_snapshot_gate != 0;
+    }
+
+    // Legacy path: lazy init (fallback when HAKMEM_ENV_SNAPSHOT_CTOR=0)
+    if (__builtin_expect(g_hakmem_env_snapshot_gate == -1, 0)) {
         const char* e = getenv("HAKMEM_ENV_SNAPSHOT");
         if (e && *e) {
-            g = (*e == '1') ? 1 : 0;
+            g_hakmem_env_snapshot_gate = (*e == '1') ? 1 : 0;
         } else {
-            g = 0;  // default: OFF (research box)
+            g_hakmem_env_snapshot_gate = 0;  // default: OFF (research box)
         }
     }
-    return g != 0;
+    return g_hakmem_env_snapshot_gate != 0;
 }
 
 #endif // HAK_ENV_SNAPSHOT_BOX_H