Phase 74-3: P0 (FASTAPI) - Free-path branch reduction optimization
Implements FASTAPI pattern to move enabled/init/stats checks outside hot loop:
- Added unified_cache_push_fast() fast-path API (no precondition checks)
- Modified tiny_legacy_fallback_free_base_with_env() to use FASTAPI with ENV gate
- Single boundary point: fallback to slow path if FULL or FASTAPI disabled
- ENV gate: HAKMEM_TINY_UC_FASTAPI=0/1 (default 0, research box)
Results (10-run Mixed SSOT, WS=400):
- Throughput: +0.32% (NEUTRAL, below +1.0% GO threshold)
- cache-misses: -16.31% (positive signal, but throughput gains insufficient)
Status: NEUTRAL, P0 FROZEN (insufficient ROI for structural change)
Next: Phase 74-4 (P2: Hot-class Inline Slots) pending per-class analysis
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Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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